So I’m dabbling with the FPS free sample game. I noticed I can create a new blank level and can add stuff it. Once it is finished, how do I “connect” it to the game? Thanks!
Once it is finished
Depends on what that means. Your could…

…once the condition is met.
Basically I want to custom build my own level and then set it up so you can use this level in the game via a portal, elevator, stairs, etc.
Cool, where do I find that example you showed?
Place a trigger in the level, right click it:
Not sure what you mean by ‘where’, though. Some reading about how levels work:
You good. I just meant where in the interface, but you showed me. Thanks! I’ll check it out!

