lessons wanted on how to debug

hello all. I am working on this script for a pool game. I'm trying to set target position to mouse click and then hit ui button to send cue ball towards target position. problem is bool is enabled when I click mouse button not the ui button and I am not sure what the target position is being set to but its not the mouse position I intended.
just need to now how to get the target position in the console view or draw a line to it or whatever I need to do to find out where I am sending the ball.

Code (CSharp):

1. public class aim : MonoBehaviour
2. {
3.  
4.     public Rigidbody rb;
5.     public bool strikeBall;
6.     private Vector3 targetPos;
7.    
8.  
9.     void start()
10.     {
11.         rb = GetComponent<Rigidbody>();
12.         strikeBall = false;
13.     }
14.  
15.     void FixedUpdate()
16.     {
17.         var mousePos = Camera.main.ScreenToWorldPoint(Input.mousePosition);
18.         var mouseDir = mousePos;
19.         mouseDir.z = 0.0f;
20.         mouseDir = mouseDir.normalized;
21.  
22.  
23.         if (Input.GetMouseButtonDown(0))
24.         {
25.             targetPos = mousePos;
26.         }
27.         if (strikeBall)
28.         {
29.  
30.             rb.AddForce(targetPos, ForceMode.Impulse);
31.         }
32.     }
33. }

any input is appreciated.

 

Use Debug.Log.