How do I Layout size , project size confused

Hello, i dont know what to do. When i set my layout size to 640,480 and project size to something much bigger , it behaves weird.

I should be only be able to see the layout(the doted lines) isnt it?. But i can see more than that. i dont get it.

and what the margins do? I dont know maybe i have encountered a bug

Layout size - Size of let's called this "area" where your game happens - think of it as a level size

Windows size - Size of your game window. How big, in pixels your game will be on preview and after export. For example 1280x720 pixels means that your game window in browser,mobile or desktop will have 1280 pixels wide and 720 pixels tall.

Margin - it's just a "free space" outside the layout in layout editor. make yourself a layout of size 400x400 and set margins to 0,0 - try pan around layout editor with Middle mouse button (or holding spacebar). Then set margins to 1000,1000, pan around, and see the difference.

Thank you that helped.