UI Button Instead of OnGUI Button need help?

Hello, I am trying to create the main menu for a game I am making. it will need to be made using unity UI but I currently have it made using OnGUI in Visual Studio and I am not sure how to make this change as I am very new to the OnGUI and I have been watching tutorials/random videos on ways around but can not find any help so I'm reaching out to anyone willing to lend me a hand.
I will need the following
- The Main Menu (With 3 buttons 1. The Host Game 2. The Join Game .3 The Exit)
- The Host Game Menu (With 4 items 1.The PlayerName 2. The Room Name 3. The Create button .4 The Back Button)
- The Join Lobby Menu (With 3 Buttons 1. The Name 2. The Select Lobby 3. The Back Button)
I Have some useful photos of my project currently this should help with an understanding of the things I need for my menu thanks
https://drive.google.com/open?id=1pjuMJRcm1mWgbNH0NvfZBMRN3DUmETsp
Here is my Room Manager Script this script has most of the code that I use for the GUI in it but I have some more I will post below
using UnityEngine;

Code (CSharp):

1.     public class RoomManager : Photon.MonoBehaviour
2.     {
3.  
4.         public string verNum = "0.1";
5.         public string roomName = "room01";
6.         public string playerName = "player 420";
7.         public Transform spawnPoint;
8.         public GameObject playerPref;
9.         public bool isConnected = false;
10.         public Transform[] spawnPoints;
11.         public bool isInRoom = false;
12.         public InRoomChat chat;
13.  
14.         void Update()
15.         {
16.             if (isInRoom)
17.             {
18.                 chat.enabled = true;
19.             }
20.             else
21.             {
22.                 chat.enabled = false;
23.             }
24.          
25.         }
26.  
27.         void Start()
28.         {
29.             roomName = "Room " + Random.Range(0, 999);
30.             playerName = "Player " + Random.Range(0, 999);
31.             PhotonNetwork.ConnectUsingSettings(verNum);
32.             Debug.Log("Starting Connection!");
33.         }
34.  
35.         public void OnJoinedLobby()
36.         {
37.             //PhotonNetwork.JoinOrCreateRoom (roomName, null, null);
38.             isConnected = true;
39.             Debug.Log("Starting Server!");
40.         }
41.  
42.         public void OnJoinedRoom()
43.         {
44.             PhotonNetwork.playerName = playerName;
45.             isConnected = false;
46.             isInRoom = true;
47.             //spawnPlayer();
48.         }
49.  
50.  
51.         public void spawnPlayer()
52.         {
53.             isInRoom = false;
54.             GameObject pl = PhotonNetwork.Instantiate(playerPref.name, spawnPoints[Random.Range (0, spawnPoints.Length)].position, spawnPoint.rotation, 0) as GameObject;
55.             pl.GetComponent<RigidbodyFPSWalker>().enabled = true;
56.             pl.GetComponent<RigidbodyFPSWalker>().fpsCam.SetActive(true);
57.             pl.GetComponent<RigidbodyFPSWalker>().graphics.SetActive(false);
58.  
59.         }
60.  
61.         void OnGUI()
62.         {
63.  
64.             if (isConnected)
65.             {
66.                 GUILayout.BeginArea(new Rect(Screen.width / 2 - 250, Screen.height / 2 - 250, 500, 500));
67.                 playerName = GUILayout.TextField(playerName);
68.                 roomName = GUILayout.TextField(roomName);
69.  
70.                 if (GUILayout.Button("Create"))
71.                 {
72.                     PhotonNetwork.JoinOrCreateRoom(roomName, null, null);
73.                 }
74.  
75.                 foreach (RoomInfo game in PhotonNetwork.GetRoomList())
76.                 {
77.                     if (GUILayout.Button(game.name + " " + game.playerCount + "/" + game.maxPlayers))
78.                     {
79.                         PhotonNetwork.JoinOrCreateRoom(game.name, null, null);
80.                     }
81.                 }
82.                 GUILayout.EndArea();
83.             }
84.             if(isInRoom)
85.             {
86.                 GUILayout.BeginArea(new Rect(Screen.width / 2 - 250, Screen.height / 2 - 250, 500, 500));
87.                 GUILayout.Box("Score: " + PhotonNetwork.player.GetScore());
88.  
89.                 if (GUILayout.Button("Spawn"))
90.                 {
91.                     spawnPlayer();
92.                 }
93.  
94.                 if (GUILayout.Button("Disconnect"))
95.                 {
96.                     PhotonNetwork.Disconnect ();
97.                     Application.LoadLevel (0);
98.                 }
99.  
100.                 GUILayout.EndArea();
101.  
102.             }
103.         }
104.  
105.  
106.     }

here is My RigidbodyFps Script some code near the bottom
using UnityEngine;

Code (CSharp):

1.   public class RigidbodyFPSWalker : MonoBehaviour {
2.  
3.         public float speed = 10.0f;
4.         public float gravity = 10.0f;
5.         public float maxVelocityChange = 10.0f;
6.         public bool canJump = true;
7.         public float jumpHeight = 2.0f;
8.         private bool grounded = false;
9.  
10.         public GameObject me;
11.         public GameObject graphics;
12.         public int health = 100;
13.         public GameObject fpsCam;
14.         private Rigidbody rigidbody;
15.         public PhotonView name;
16.         public bool isPause = false;
17.         public AudioSource sound1;
18.         public AudioClip soundClip;
19.         public GameObject ragDoll;
20.  
21.  
22.         void Awake()
23.         {
24.             name.RPC("updateName", PhotonTargets.AllBuffered, PhotonNetwork.playerName);
25.             rigidbody = GetComponent<Rigidbody>();
26.             rigidbody.freezeRotation = true;
27.             rigidbody.useGravity = false;
28.         }
29.  
30.         void FixedUpdate()
31.         {
32.             if (grounded)
33.             {
34.                 // Calculate how fast we should be moving
35.                 Vector3 targetVelocity = new Vector3(Input.GetAxis("Horizontal"), 0, Input.GetAxis("Vertical"));
36.                 targetVelocity = transform.TransformDirection(targetVelocity);
37.                 targetVelocity *= speed;
38.  
39.                 // Apply a force that attempts to reach our target velocity
40.                 Vector3 velocity = rigidbody.velocity;
41.                 Vector3 velocityChange = (targetVelocity - velocity);
42.                 velocityChange.x = Mathf.Clamp(velocityChange.x, -maxVelocityChange, maxVelocityChange);
43.                 velocityChange.z = Mathf.Clamp(velocityChange.z, -maxVelocityChange, maxVelocityChange);
44.                 velocityChange.y = 0;
45.                 rigidbody.AddForce(velocityChange, ForceMode.VelocityChange);
46.  
47.                 // Jump
48.                 if (canJump && Input.GetButton("Jump"))
49.                 {
50.                     rigidbody.velocity = new Vector3(velocity.x, CalculateJumpVerticalSpeed(), velocity.z);
51.                 }
52.             }
53.  
54.             if (Input.GetKeyDown(KeyCode.Tab))
55.             {
56.                 isPause = true;
57.             }
58.             if (Input.GetKeyUp(KeyCode.Tab))
59.             {
60.                 isPause = false;
61.             }
62.  
63.             // We apply gravity manually for more tuning control
64.             rigidbody.AddForce(new Vector3(0, -gravity * rigidbody.mass, 0));
65.  
66.             grounded = false;
67.  
68.             if (health <= 0)
69.             {
70.                 GetComponent<PhotonView>().RPC("DIE", PhotonTargets.AllBuffered, null);
71.             }
72.         }
73.  
74.         void OnCollisionStay()
75.         {
76.             grounded = true;
77.         }
78.  
79.         float CalculateJumpVerticalSpeed()
80.         {
81.             // From the jump height and gravity we deduce the upwards speed
82.             // for the character to reach at the apex.
83.             return Mathf.Sqrt(2 * jumpHeight * gravity);
84.         }
85.  
86.         private void OnGUI()
87.         {
88.             GUI.Box(new Rect(10, 10, 100, 30), "HP | " + health);
89.  
90.             if (isPause)
91.             {
92.                 GUILayout.BeginArea(new Rect(Screen.width / 2 - 250, Screen.height / 2 - 250, 500, 500));
93.                 foreach (PhotonPlayer pl in PhotonNetwork.playerList)
94.                 {
95.                     GUILayout.Box(pl.name + " | " + pl.GetScore());
96.                 }
97.                 GUILayout.EndArea();
98.             }
99.         }
100.  
101.         [PunRPC]
102.         public void applyDamage(int dmg)
103.         {
104.             health = health - dmg;
105.             Debug.Log("hit!" + health);
106.         }
107.  
108.         [PunRPC]
109.         public void DIE()
110.         {
111.             if(GetComponent<PhotonView> ().isMine)
112.             {
113.                 Destroy(me);
114.                 Destroy(ragDoll, 3);
115.                 GameObject rDoll = PhotonNetwork.Instantiate(ragDoll.name, transform.position, transform.rotation, 0);
116.                 PhotonNetwork.Destroy(me);
117.                 GameObject.Find("_ROOM").GetComponent<RoomManager>().OnJoinedRoom();
118.             }
119.         }
120.  
121.         public void getClip (AudioClip soundToRecieve)
122.         {
123.             soundClip = soundToRecieve;
124.         }
125.  
126.         public AudioClip[] sounds;
127.  
128.         [PunRPC]
129.         public void playSound()
130.         {
131.             sound1.PlayOneShot (soundClip);
132.         }
133.     }

And here is my playername Script

Code (CSharp):

1. using UnityEngine;
2.     using UnityEngine.UI;
3.  
4.     public class playerName : MonoBehaviour
5.     {
6.         public Text nameTag;
7.  
8.         [PunRPC]
9.         public void updateName(string name)
10.         {
11.             nameTag.text = name;
12.             Debug.Log(nameTag.text);
13.         }
14.     }