How to go about doing health

Here is a simple C# script that often use as the base for my health systems. It'll need to be expanded quite a bit to actually work in a game but it should give you and a basic idea of how something like this works.

 using UnityEngine;
 using System.Collections;
 
 public class playerHealth : MonoBehaviour {
  #region editor_vars
  public int Health;
  #endregion
  
  #region priv_vars
  private bool life;
  #endregion
  
  void Start () {
  life = true;
  }
  
  void Update () {
  if (!life) {/*What do we do? WE DIE?!?*/}
  }
  
  public void takeDamage (int lowDmg, int highDmg) {
  int damage = Random.Range(lowDmg, highDmg);
  Health -= damage;
  }
  
  public void takeDamage (int lowDmg, int highDmg, out int damageDone) {
  int damage = Random.Range(lowDmg, highDmg);
  damageDone = damage;
  Health -= damage;
  }
  
  public void getLife (int lifeBack) {
  Health += lifeBack;
  }
 }

You're not going to want to leave that life check inside update. It's just easy to prototype that way. Less junk to wire together until you're worried about performance later on down the line.