unity when to use coroutines code example

Example 1: unity coroutine

void Start() {
  StartCoroutine("func"); // Start coroutine named "func"
}

IEnumerator func() {
  Debug.Log("Hello");
  yield return new WaitForSecondsRealtime(1); //Wait 1 second
  Debug.Log("World");
}

Example 2: how to write coroutine in unity

using UnityEngine;
using System.Collections;// In this example we show how to invoke a coroutine and execute
// the function in parallel.  Start does not need IEnumerator.public class ExampleClass : MonoBehaviour
{
    private IEnumerator coroutine;    void Start()
    {
        // - After 0 seconds, prints "Starting 0.0 seconds"
        // - After 0 seconds, prints "Coroutine started"
        // - After 2 seconds, prints "Coroutine ended: 2.0 seconds"
        print("Starting " + Time.time + " seconds");        // Start function WaitAndPrint as a coroutine.        coroutine = WaitAndPrint(2.0f);
        StartCoroutine(coroutine);        print("Coroutine started");
    }    private IEnumerator WaitAndPrint(float waitTime)
    {
        yield return new WaitForSeconds(waitTime);
        print("Coroutine ended: " + Time.time + " seconds");
    }
}