In Windows: If you followed the instructions above to install git, you should have a terminal called Git Bash installed on your system. To open it, go to the Start menu and search for Git Bash. Click on the application to open it.
In macOS: You already have the Bash terminal installed on your system, so you can simply open it. If you have never used it before, you can find more information here.
In Linux: You already have the Bash terminal installed on your system, so you can simply open it. If you have never used it before, you can find more information here.