Window managers (short WM) are the cool guys that arrange your different windows on the screen.
There are three types of window managers:
- Stacking window manager: windows can stack on top of each other, like pieces of paper on a desk and just like on default Windows and macOS; also known as floating window managers.
- Tiling window manager: “tiles” the windows so that none of them overlap and are visible at all times.
- Dynamic window manager: can have both stacking and floating windows.
Desktop environments come with their own. For example:
- GNOME comes with Mutter;
- KDE, with Kwin.
These are stacking window managers.
You can however pick your own window manager, whether you are already on a desktop environment or not! Why would you want do so? Well, maybe you want to swap to a tiling window manager, which will give you:
- more efficient use of screen space: not having to ALT+TAB through every hidden window;
- more keyboard-centric actions (usually faster than with a mouse);
- more performance and less pressure on system resources!
They don't often play a major role in gaming, except when you choose the Wayland display server! In that case: they are better known as compositors, not to confuse with X11 compositors.
On desktop environments
First off: you may not have the cleanest experience.
Window managers are usually built around their respective desktop environments. By changing the WM, you can end up with user interface discrepancies; but with some changes, plus obviously the functionality you're seeking out of a WM, you will feel right at home!
Instead, you might want to go...
Outside desktop environments
This allows for the cleanest experience.
For this, you will need a Linux distribution that allows you to choose your own window manager. Either one with a predefined set, or either one which lets you install what you want: the latter will demand more time and effort.
About other applications like file managers and internet browsers: not all of them are optimized to be run in a standalone window manager. This can result in unusable programs. Even though these problems can be fixed, you still need to know how. On top of that, window managers don't come with any programs preinstalled. You need to know what you want to use. If you do not use a common desktop environment, this might seriously harm your experience. If you just want something that works, use a desktop environment, for example KDE or Gnome.