Aspect Ratios And Fullscreen Preview

I noticed that I can preview my game in different aspect ratios. Is it the aspect ratio of the screen (like how the game would look on this type of screen) or of the camera (would look the same on all screens)? And what is "free aspect", and what is "standalone"?

My game is supposed to word on different screens.
Should I do something special to allow support for different resolutions aspect ratios etc?

How do I preview my game in full screen? I have put the following script on the main camera, but there is no effect.

function Update () {
    Screen.fullScreen = true;

It's the aspect ratio of the screen. Free aspect means you can resize the window to whatever; standalone is constrained to whatever you have the resolution set to in the player settings. Whether you should do something special depends on what you're doing exactly. Any GUI stuff should be programmed to be aspect-ratio independent, at least. There is no full-screen preview in the editor; the most you can do is use maximize on play.