How to Make Health Bar in Unity

The health bar is suitable for determining the amount of health of enemies or the main character. The health bar changes color depending on the amount of health to green, yellow, red.

Steps

Create script HealthBar.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityEngine.UI;

public class HealthBar : MonoBehaviour
{
    [SerializeField] private int _health = 100;
    [SerializeField] private Slider _healthBar;

    private int _healthMax;

    private void Start()
    {
        SetHealth(_health);
    }

    public void TakeDamage(int damage)
    {
        if (_health > 0)
        {
            _health -= damage;
            _healthBar.value -= (float)10 / Mathf.Pow(10, _healthMax.ToString().Length - 1);
        }

        if (_health <= 0)
        {
            Death();
        }

        ChangeHealthBarColor();
    }

    public void SetHealth(int health)
    {
        _healthBar.value = health;
        
        if(_health > _healthMax)
        {
            _health = _healthMax;
        }

        ChangeHealthBarColor();
    }

    private void Death()
    {
        Destroy(this.gameObject);
        Debug.Log("Dead");
    }

    private void ChangeHealthBarColor()
    {
        Color color;

        if (_healthBar.value > 0.5)
        {
            color = Color.green;
        }
        else if ((_healthBar.value > 0.25f) && (_healthBar.value <= 0.5f))
        {
            color = Color.yellow;
        }
        else
        {
            color = Color.red;
        }

        _healthBar.fillRect.GetComponent<Image>().color = color;
    }
}

Create Canvas in Inspector > Canvas > Render Mode choose World Space
Create Enemy object and add Canvas to object

Download

Health Bar Download