You can download Prolog or use the online version (SWISH). But I don't want you to use the online version for your homework assignments or tests.
On Windows, the download version comes with a console user interface and graphical (window) user interface.
The Mac/Unix version only has the console user interface.
The graphical user interface is very primitive and comes bundled with an ancient EMACS editor, so you might be better off with the console version.
Here are the instructions on starting Prolog.