Destroying Enemy

hi guys im new to unity and i want to ask how do i destroy the enemy in my fps game? currently when i start the game once i clicked on fire whether i hit the enemy or not it just dissapears.

using UnityEngine;
using System.Collections;

public class shoot : MonoBehaviour {

public GameObject bullet;
public GameObject bulletHole;
public float delayTime = 8;

private float counter = 0;

// Use this for initialization
void Start () {

}

// Update is called once per frame
void FixedUpdate () {
	if (Input.GetKey (KeyCode.Mouse0) && counter > delayTime ) {
		Instantiate(bullet, transform.position, transform.rotation);
		audio.Play();
		counter = 0;

		RaycastHit hit;
		Ray ray = new Ray(transform.position, transform.forward);
		if(Physics.Raycast(ray, out hit, 100f)) {
			Instantiate (bulletHole, hit.point, Quaternion.FromToRotation(Vector3.up, hit.normal));
			Destroy (GameObject.FindWithTag("enemy"));
		}
	}
	counter += Time.deltaTime;

}

}

Hey. Looks like this is your gun script, correct? Anywho. The gun should not handle the raycast detection. Also you are casting the ray from your gun, not the bullet.
transform represents the controller of this script so instead of running it like that, you should create a separate script attached to your bullet that casts a ray from the bullet’s origin outward and when it detects the enemy (by tag or whatever), destroy the enemy.
But instead of searching for the enemy by its tag, Destroy the hit.gameObject. This will guarantee that you do not destroy some other random enemy.

It’s because you’re not checking what the raycast is hitting. It could be hitting a wall and not the enemy, and the enemy would still be destroyed.

if (Physics.Raycast(ray, out hit, 100f)) {
    if (hit.collider.CompareTag("enemy)) {
        Instantiate(bulletHole, hit.point, Quaternion.FromToRotation (Vector3.up, hit.normal));
        Destroy(hit.collider.gameObject);
    }
}

By the way, you want to destroy the enemy the same way this code does, because if there’s multiple enemies the first one that is found will be destroyed, not necessarily the one that got hit.