What is the difference between Git GUI, Git Bash and Git CMD? I'm a beginner, and for doing my installations I usually find myself using both git bash and git CMD
Git CMD is just like regular Windows command prompt with the git command. It lets you use all of Git features through command line. Useful if you are already familiar with Windows cmd and you only work on Windows.
Git Bash emulates a bash environment on windows. It lets you use all git features in command line plus most of standard unix commands. Useful if you are used to Linux and want to keep the same habits.
Git GUI is a Graphical User Interface letting you use Git without touching command line. It is an alternative among other Git clients. Since Git GUI is very minimal, you could also look at other alternatives if GUIs interest you.
It is up to you to decide which you want to use. As many others, I recommend you to learn Git with command line before switching to a graphical interface. If you don't know which to choose between Git Bash and Git CMD, I'd go for Git Bash since bash is a really useful tool to learn.