Can you use the source from the FPS tutorial?

Hello, I have been testing out this engine, and I'm really liking it. The game i intend to make essentially needs the exact gameplay elements that are included in the tutorial for making an FPS. Am I legally allowed to just copy paste the parts of that demo/tutorial that I want and give credit? It sounds like it from all of the talk of "publishing" at the end of the tutorial.


Thanks.