AI Enemy Collision Detection

Im trying to code an ai enemy, but cant figure out how to include collision. I tried setting Character collision detection 2d as a boolean, but that raised a lot of error messages. Any ideas?

Code (CSharp):

1. using System.Collections;
2. using System.Collections.Generic;
3. using UnityEngine;
4.  
5. public class Alien1 : MonoBehaviour
6. {
7.     public Vector2 moving = new Vector2();
8.     // Start is called before the first frame update
9.     void Start()
10.     {
11.  
12.     }
13.  
14.     // Update is called once per frame
15.     void Update()
16.     {
17.  
18.         public bool collisionDetection = CollisionDetectionMode2D
19.  
20.         moving.x = moving.y = 0;
21.  
22.         if (collisionDetection = false)
23.         {
24.             moving.x = 1;
25.         }
26.         else if (collisionDetection = true)
27.         {
28.             moving.x = -1;
29.         }
30.  
31.     }
32. }
33.