I am new to nixos too. As for flakes, it is little complicated at least for me. Vimjoyer video helped me understand little about flake. Here the link www.youtube.com/watch?v=JCeYq72Sko0You can go through his nixos series. And there another YouTuber librephoenix. He has good learning material too. Here is link www.youtube.com/channel/UCeZyoDTk0J-UPhd7MUktexw