The most common use of a Ray from the camera is to perform a raycast out into the scene. A raycast sends an imaginary "laser beam" along the ray from its origin until it hits a collider in the scene. Information is then returned about the object and the point that was hit in a RaycastHit object. This is a very useful way to locate an object based on its onscreen image. For example, the object at the mouse position can be determined with the following code:

using UnityEngine;using System.Collections;public class ExampleScript : MonoBehaviour {	public Camera camera;	void Start(){		RaycastHit hit;		Ray ray = camera.ScreenPointToRay(Input.mousePosition);				if (Physics.Raycast(ray, out hit)) {			Transform objectHit = hit.transform;						// Do something with the object that was hit by the raycast.		}	}}