I need advice for my CS NEA

My project is on an fps game. What’s the baseline of what’s not allowed when using loads of tutorials to learn how to code a game? I’ll of course show references of using the sources to because then that would be plagiarism, as it’s not my original work. But how do I know what’s okay to use? E.g. would I be allowed to use someone’s code for a procedural dungeon generator or would I have to do it by scratch? Would I need to do all the 3D rendering of models or can I just use the assets/presets from said Unity?