Full screen youtube video

From what i saw, if i click on full screen to watch a video, it created a whole new desktop, what happens if i exit the full screen video? Does it go back to my browser and close that desktop or does it keep it open but empty? Or what? I’m about to buy a macbook but it had so many annoying features like this and also the inability to open 2 windows side by side and move the mouse freely between them to click on stuff ONCE, and not having to click once to be in that window and click AGAIN to use whatever u were going to use on that particular window.