Yeah, I’m new to using the Panda3D library, no need to welcome me.
Before I use it, I’m trying to understand the licensing of the software. I get that it is a modified BSD license, but is there some sort of fine print I need to read up on? Like what conditions I have to meet to make my programs commercially avaliable?
Whatever I have to learn about it would be appreciated.
Welcome to the forums!
Seen this page?
panda3d.org/license.php
As long as you obey those three simple rules, you should be fine. 
But do I have to include Panda3D or anything it uses into my documentation?
That’s something I noticed in BSD licenses.
You must include the license text somewhere indeed. You can just put it in a text file and ship it somewhere with your game. No need to put a big “made with panda3d” banner somewhere (even though that would be appreciated).
Here’s another question about documentation:
If I was to sell my game for example on Steam, how exactly would documentation be written? Where would it have to be stored and how would it have to be written?
This doesn’t seem license related, and the answer is that you can probably do it in any form you like. From documents attached to the game to inline help or online help.