How do I delete a bullet clone when it touches a game object or wall?

gameObject refers to the object that script is attached to. Make sure you use that function in right script. Or you can use;

 void OnTriggerEnter(Collider collider){
    Destroy(collider.gameObject) //the object that collided with your character.
 }

When you mean clones are u meaning Prefabs? if so please give me both scripts you have written

@Lifes_great

This is the code I used to make the bullet shoot. (got it from a Brackeys video)

public Transform firePoint; public GameObject bulletPrefab;

 public float bulletForce = 20f;

 // Update is called once per frame
 void Update()
 {
     if (Input.GetButtonDown("Fire1"))
     {
         Shoot();
     }         
 }

 void Shoot()
 {
     GameObject bullet = Instantiate(bulletPrefab, firePoint.position, firePoint.rotation);
     Rigidbody2D rb = bullet.GetComponent<Rigidbody2D>();
     rb.AddForce(firePoint.right * bulletForce, ForceMode2D.Impulse);
 }

 

}