It seems that you mix up GameObjects and Prefabs.
When you say "Prefabs in another scenes" I think you are talking about Game Objects.
Game Objects are objects, prefabs or not, who are in a scene. Prefabs are Game Objects that can be "saved" in your game folder. You can find more about Prefabs here.
That said, and if I understand your question correctly, you want to instantiate Prefabs in your scene.
First of all you need to make the GameObject you want to instantiate a Prefab. Go to the scene where the GameObject you want is, and simply drag and drop it in the Unity Project View (where your game folder is). It should now be blue in the scene hierarchy, and visible as a prefab in the folder you dropped it in.
Now go back to the scene where you want to instantiate it. You have 2 options. One via the Editor and one programmatically (in fact you have another option using the Resources.Load but I won't explain it here).
1. Via the editor
To put a prefab in your scene, just click on it in the game folder (in the Project View) and drag it to the Hierarchy view. That's it. Your prefab is now a Game Object of your scene.
2. Via script
In a script of yours (a Monobehaviour) you can declare a prefab entry such as:
public Transform my_prefab;
Now, if you link your script to a GameObject you will see an empty entry called my_prefab. Just drag your Prefab to that entry to fill it with the Prefab you want to instantiate. Later in your code you can instantiate it, in the Start method of your script for example, using:
private void Start()
if ( my_prefab != null ) // check that the prefab is set.
Now, at Start, the prefab you have chosen will be instantiated in your scene.
I hope it helps.