If you're using a mainstream desktop Linux - Debian, Ubuntu, Raspbian, Fedora, etc. - then you can probably just use your package manager and be up and running in a few minutes. For example, on most of my machines, I would open a terminal (Gnome Terminal, xterm, LXTerm, etc.) and type:

sudo apt-get update
sudo apt-get install git git-gui gitk

sudo apt-get update
sudo apt-get install git git-gui gitk

On an RPM-based distribution, I would do:

sudo yum install git git-gui gitk

sudo yum install git git-gui gitk

You can also install from source, but usually that should be unnecessary unless your system is very out of date.

Notice those extra packages, git-gui and gitk? You might as well leave those off if you're running a text-only system (like a Raspberry Pi that you only access over a console cable), but on graphical desktops they're helpful tools for quickly committing work and reviewing history.