Todd,
I’m not a 100% sure I understand your question. So I hope this helps.
Project File – This is your whole project. You can only have one project file open at a time.
Composition – This is where you are building your project inside your “Project File”
Pre-Composition – Think of it as nesting a composition inside a composition. This is really handy for organizing a complicated project so you have fewer layers. It is also a great way to apply something like a position keyframe or effect once since it will affect everything in the pre-comp.
As for a HUD tutorial, I think you are asking for one? If yes check this out: https://www.videocopilot.net/tutorials/futuristic_hud/
I hope this post was of a little help.
Stephen Smith
Utah Video Productions
Check out my Vimeo page