How to make enemys do damage and you dying etc

So I have a zombie arcade game in 3d, zombies can die, i do dmage, they fallow me, alls good. I Besides I need the zeds to be able to kill me as in 4 hits to me ends the game and switches to a GAME OVER scene. doesnt sound too complicated but ive been stuggling with this for the past 2 weeks. Also I would like if on each of the 4 hits blood goes on the screen and it gets redder (like in cod haha). Thanks anyone who helps!
Heres my EnemyController Script:

    using UnityEngine;
    using System.Collections;
    using UnityEngine.AI;
    
    public class EnemyController : MonoBehaviour {
    	NavMeshAgent nav;
    	Transform player;
    	Animator Controller;
    
    	// Use this for initialization
    	void Awake () {
    		nav = GetComponent <NavMeshAgent> ();
    		player = GameObject.FindGameObjectWithTag ("Player").transform;
    		Controller = GetComponentInParent<Animator> ();
    	}
    
    	// Update is called once per frame
    	void Update () {
    		nav.SetDestination (player.position);
    		Controller.SetFloat ("speed", Mathf.Abs (nav.velocity.x + nav.velocity.z));
    	}
    }

HERES MY GAME MANAGMENT SCRIPT IF YOU MAY NEED IT?

    using System.Collections;
    using UnityEngine;
    
    public class GameManagment : MonoBehaviour {
    	public int round = 1;
    	int zombiesInRound = 10000000;
    	int zombiesSpawnedInRound = 0;
    	float zombieSpawnTimer = 0;
    	public Transform[] zombieSpawnPoints;
    	public GameObject zombieEnemy;
    
    	// Use this for initialization
    	void Start () {
    
    	}
    
    	// Update is called once per frame
    	void Update () {
    		if (zombiesSpawnedInRound < zombiesInRound)
    		{
    			if (zombieSpawnTimer > 2.1)
    			{
    				SpawnZombie ();
    				zombieSpawnTimer = 0;
    			}
    			else
    			{
    				zombieSpawnTimer += Time.deltaTime;
    			}
    		}
    	}
    
    	void SpawnZombie()
    	{
    		Vector3 randomSpawnPoint = zombieSpawnPoints [Random.Range (0, zombieSpawnPoints.Length)].position;
    		Instantiate(zombieEnemy, randomSpawnPoint, Quaternion.identity);
    		zombiesSpawnedInRound++;
    	}
    }

look up speed tutor on youtube he does some of these things and as for health and such its very difficult good luck