how do i make it so when i click on an object it sets it as a variable

hey, i want to make some sort of way to target objects kind of like in bf3 when you lock someone with a missile. basicaly i have no idea on how o make it so when the object is in an specific area of the screen, marked by a GUI it locks it after a few seconds. if some one has an idea on how to make this pls tell me. thank you

Blablabla… target script! Asho3$! cant anyone post a freeken answer on here to actually help anyone out? Anyways here is my target script. I got it in a tutorial some where.

>     using UnityEngine;
>     using System.Collections;
>     
>     public class Ray1 : MonoBehaviour {
>     	public string target;
>     	public GUISkin SkinTarget;
>     	void Start () {
>     	
>     	}
>     
>     	void Update () {
>     		if (Input.GetButtonDown ("Fire1")) {
>     						RaycastHit hit;
>     						Ray ray1 = Camera.main.ScreenPointToRay
> (Input.mousePosition);
>     						if (Physics.Raycast (ray1, out hit))
>     				target = hit.transform.name;
>     		}
>     	}
>     	//public float vSliderValue = 0.0F;
>     	void OnGUI () {
>     		GUI.skin = SkinTarget;
>     		GUI.Box(new Rect(25, 10, 200, 200), "Target : " +target);
>     		//vSliderValue = GUILayout.VerticalSlider(vSliderValue,
> 0.0F, 1500.0F);
>     	}
>     }