Cient folder will hold all of the frontend "client" code that is displayed to the user. There is a readme inside /client regarding how to start up the react app on your local server. You may have to install node first, which there are a bunch of online tutorials about. Go to nodejs website, and download the LTS (long-term support) version.
Inside client, the actual code will be stored inside /src. React files are known as components, so the main parts of the actual frontend will be in /components. When you start the local server, you can currently click on the two buttons to either go to the student or professor portals, depending on what you're assigned.