In my pong game How do I prevent paddle from going threw walls?

You can use either (this is up to personal preferences):

Rigidbody + collider

You can setup colliders for your paddle and wall.

Pros :

• Automated process, no scripting

Cons :

• You will get a jerking motion when you are trying to go through the wall

  Limit position via value clamping

Since this a pong game, you can use a simple calculation to limit the position of your paddle at the certain axis.

 public class Control : MonoBehaviour {
    public Transform paddle;
    public float upperLimit, lowerLimit;
 
    void Update() {
    
       //Process the moving paddle here (your current code)
       ...
 
       //Finalize/Limit the paddle position (in this example, y axis)
       //  You can do this seperately, or you can incorporated
       //  this into the moving code
       Vector3 pos = paddle.position;
       pos.y = Mathf.Clamp( pos.y, lowerLimit, upperLimit );
       paddle.position = pos;
    }
 
 }

Pros :

• No jerking motion ( the jerking motion is caused by the re-position of the gameObject when it is forced through another collider )

• More control

Cons :

• Need to be re-adjusted for different wall distance ( negligible )