What does Make Sticky mean?

Also, will classmates will able to add additional forums or only add to the ones I have created

"Make Sticky" tacks your post to the top of the page. It's helpful for things like forum instructions, or other things that are important that you want to remain at the top of your page at all times. "Sticky" posts don't get shoved down by subsequent new posts like regular posts do.

No, only Administrators can actually create the forum categories themselves. Classmates can post new topics within each forum, but the number of individual forum discussion topics you have is entirely up to you, the Administrator.

Thank you for the plain English response! We just created the new message forum and I'm sure I'll be asked this question tomorrow. I'll probably be back with more simple questions later!