GUI
Graphical User Interfaces
Linux is great as a server with only using a CLI. A GUI uses resources, and with a server do you really need a GUI?
Linux also works great as a workstation and personal desktop OS. As end users we need to have access to a GUI (we've become spoiled over the years). Linux has a LOT of different GUIs you can pick from. Keep in mind though, that not all GUIs are equal. You might have a Desktop Environment (which is probably what you are most use to with using Windows or MacOS) or you can have a very simple Window Manager (great for older systems, as it doesn't require as many resources).
Desktop Environment: A desktop environment provides a common graphical user interface across multiple applications. This includes icons, toolbars, and widgets. Plus, a desktop environment includes its own window manager!
Window Manager: Very simple graphical user interface that is able to control the placement of windows. A window manager controls the border, title bar, size and resizing ability. A window manager is a very simple GUI.
In this section we will not talk about all the GUI options, but we will cover the basics of configuring a GUI. Please make sure to read each of the following URLs to learn about configuring XWindows and GUI options in Linux.
This is deprecated, but worth including for historical purposes and older distros.
Each distribution usually has their own help with this.
If you are going to use a GUI you will probably want to also install a display manager. A display manager can allow you to pick a different Desktop Environment or Window Manger. Linux is pretty awesome as you can have a different GUI installed for different users! For example, I might want to use KDE, but you want to use gnome. This is possible in Linux with a display manager installed.
Configure GDM (this is a long web page with a lot of details, feel free to skim it)
LightDM is becoming more popular recently.