How do I add a forum so that all my classmates can see it? I viewed the help video, but Admin Forums doesn't have all the options shown in the video.

When I click on Admin Forums, I'm taken to a page with a discussion named General Admin Forum. I was easily able to create another discussion that I titled High School Stories.

When I clicked on Add/Edit Forums, I selected Hight School Stories. That allows me to edit the discussion name, enter a description, add a password, make in read only, and make it active (yes/no).

When I went to Forum Preferences, I have only two options, Admin Forums Yes/No and to rename the discussion.

I can't seem to find a way to create a forum that all registered classmates can take part in.

What you want is a function/page called "User Forums". It's not automatically included for newer sites, but can be added on request.

Just activate the "User Forums" and "Message Forums" that can be found at the bottom of your Edit Site Pages administrator page.