If anybody knows how, please please please tell me is there a way to add a menu or a gui interface/hud or something please? Thanks
You have to do it manually, for example buttons as sprites, and everything in a new layer, so while you don’t move the camera of this new layer, the GUI will stand in the screen.
Then you can check if the mouse button has been released over a button, if so, launch actions related to such button (change scene, switch fullscreen, quit the game).
Let me know if something is not clear 
THIS is actually great cause i was searching myself own to create a menu let’s start with the quit button can i use the same C# code or I’ll have to use something else?
No you can’t use C#.
In theory, you can use C++ in native games and JavaScript in HTML5 but a quit button is really simple to do using events.
To create a quit button the only thing you need to do is place a sprite in to your scene used as the quit button and create this event:
If the cursor/touch is on quit button and Left mouse button was released : Quit the game