Instantiate prefabs by different types?

I feel this is very basic, but I just can't figure it out.

In this video:

The script looks like this

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class UsingInstantiate : MonoBehaviour
5. {
6.     public Rigidbody rocketPrefab;
7.  
8.     void Update()
9.     {
10.         if(Input.GetButtonDown("Fire1"))
11.         {
12.             Instantiate(rocketPrefab);
13.         }
14.     }
15. }

The "rocketPrefab" is initialized as a Rigidbody, but the prefab is a GameObject, maybe with a Rigidbody attached, isn't it?

Why do this code not initialize "rocketPrefab" as a GameObject?

I am trying to do this:

Code (CSharp):

1. using UnityEngine;
2. using System.Collections;
3.  
4. public class Spawn : MonoBehaviour {
5.    
6.     public GameObject prefab;
7.    
8.     void Start () {
9.  
10.         GameObject test = Instantiate (prefab) as GameObject;
11.         test.tag = "TagName";
12.     }
13.    
14.     // Update is called once per frame
15.     void Update () {
16.  
17.     }
18. }

The prefab is Instantiated, but I can't set the tag name?

As mentioned, would it be nice to understand this. I feel I lack some basic understanding.

Thanks

 

u should check if u have the Tag named "TagName"

 

I have. The error I get is this:

"NullReferenceException: Object reference not set to an instance of an object"

 

if u have the prefab?it means the prefab is null;

 

But the prefab is Instantiated and live on my scene. Should "test" not be a direct reference to the GameObject?

 

I had to call it like this

test.gameObject.tag = "TagName";