Firstly, if you haven't already done so, you need to download and install Git. The download is available at https://git-scm.com/download/win, and it should start automatically when you visit that page. Run the file that's downloaded, and the setup will start (if a notice says this isn't verified then tap the Install Anyway button). The default options should work for most users—make sure that Use Git from the Windows Command Prompt is selected to avoid more work later on.

Once this is completed, open a Command Prompt window (search for cmd from the Start menu if you don't have a shortcut) and type git --version—you should see something like the following output: