Hi guys I am wondering how can I stop the audio from playing if I click the object twice?

This is the Script that I am using

using UnityEngine;
using System.Collections;

public class OnMouse_playAudio : MonoBehaviour {


	// Use this for initialization
		// Use this for initialization
	void Start () {

	}
	
	void OnMouseDown()
{     
    audio.Play();
}
	

}

to stop your audio, use audio.Stop();
see Unity - Scripting API: AudioSource.Stop

To start on one click and stop on the next, use a boolean

if you don’t know what a boolean is or how to use one, I strongly suggest you start with this book:

This might work.

using UnityEngine;
using System.Collections;
 
public class OnMouse_playAudio : MonoBehaviour 
{
	bool audioBool = false;
 
    void OnMouseDown()
	{     
    	audioBool = !audioBool;
    	
    	if(audioBool)
 			audio.Play();
		else
			audio.Stop();
	}
}