load scene by index unity code example

Example 1: how to get scene index unity

SceneManager.GetActiveScene().buildIndex;

Example 2: loadscene unity

using UnityEngine;
using UnityEngine.SceneManagement;

public class Singleplayer : MonoBehaviour
{
    public void LoadNextLevel()
    {
    	//This will load the next scene in the buildIndex, e.g if in scene 3, go to scene 4
        SceneManager.LoadScene(SceneManager.GetActiveScene().buildIndex +1);
    }
}