I'm very new to Game Jams, this is my first one, and new to game dev in general. So I don't really know what a publicly available library is. Can you give me a super quick explanation?

I think by 'publicly available library' he means like 3rd party libraries you can find online.

For example your game engine might not have water physics built in, so you might be able to download a public library from online that contains the code you can put into the game.

First of all congratulations on doing your first game jam, hope you have a good time this weekend.
By this I essentially mean any codebase, engine, or library that anyone could download off of a public site. So no codebases that you happened to have before the jam unless they are available for others to download online as well.

Ok. I guess what I meant by this post is; Can I use the pre-made Unity FPS Controller and a few other built in Unity assets?