A monitor, TV, or any type of virtual screen or other device meant to project video from the computer is considered a ‘display’ on a Linux system. In some contexts, it may also be referred to as a ‘screen,’ but you get the idea. We can check which displays are connected to Linux using a few different methods. This can help us determine information about detected displays, connected screens, and troubleshoot problems with video not displaying (whether it be physical or over a network).
A window manager is the portion of a GUI (graphical user interface) responsible for the placement, functionality, and appearance of windows. They typically allow a user to control things like dragging a window around, resizing it, turning borders on or off, etc. Window managers are frequently built into the desktop environment itself, but some are available for standalone installation and will give you a different experience while still working with the same components throughout the rest of the GUI.