How do I make a camera in the background of my menu gui?

For example: In the background of the gui, theres an camera that shows an certain position of your place, and then when you click Start it goes away and you get set to your default camera, your character.

You may create a LocalScript inside the Gui object, that when it loads, changes the camera properties.

First, the CameraType.

game.Workspace.CurrentCamera.CameraType = "Scriptable"

Then its position.

game.Workspace.CurrentCamera.CoordinateFrame = CFrame.new( the cframe position you want )

And when you click the Start button (using a MouseButton1Click event, for example), you reset the camera to your character.

game.Workspace.CurrentCamera.CameraSubject = game.Players.LocalPlayer.Character.Humanoid
game.Workspace.CurrentCamera.CameraType = "Custom"

If it's difficult for you to determinate the camera CFrame, go to studio and place the camera in the position you want and enter this in Command Bar.

print(game.Workspace.CurrentCamera.CoordinateFrame)

Then you copy it from the output and insert it in CoordinateFrame.

If you want more complicated stuff, try the wiki: http://wiki.roblox.com/index.php?title=Camera_manipulation