AQA Computer Science NEA Help

My NEA for computer science is due next week and I was hoping for some help. Our teachers really haven't given us any guidance for our documentation and I was wondering specifically how in depth the documentation needs to be. I'm aware that we're meant to add code explanations but how in depth do they need to be, (like line by line or a more generic overview of how they work so most people could understand) and also do we need them for every piece of code, or just for the pieces that are the most complicated. Equally if a piece of code is complicated but more for how long it is as opposed to the code itself being complex, is that something we need to explain as well?