How to instantiate particle in touch position?

Hello i am beginner in unity! I read many questions and answers and I could not find right answer for this. I want to emit stars on the touched position in mobile.
What I tried for instantiating the particle is like this :

public class StarEmit : MonoBehaviour {
private Touch touch;
	void Start () {
touch = Input.GetTouch(0);
	}
	void Update () {
float  x = touch.position.x/ Screen.width;
float y = touch.position.y/ Screen.height;
transform.position = new Vector3(x,y,0);
	}
}

You should get touch position inside Update() method and not in Start() as Start() is executed only once and not per frame. So your code should be:

 public class StarEmit : MonoBehaviour {
    Touch touch;
     void Update () {
         if(Input.touchCount > 0)
         {
             touch = Input.GetTouch(0);
          }
         float  x = touch.position.x/ Screen.width;
         float y = touch.position.y/ Screen.height;
         transform.position = new Vector3(x,y,0);
     }
 }

The code above will teleport the transform of gameobject to touch position. If you want to smoothly move the transform then you should consider using Vector3.Lerp.