CSS Deep Dive is Incomplete-Grids

In the first project conducted by Nick Pettit namely "Build a Simple Website" Mr, Nick tells us about using grids and saying that it is an advanced topic suggests on simply using pre-made grids. However in CSS Deep Dive this topic was not covered. Honestly speaking, by the end of html and css deep dives we should know everything to create the front end of a "simple" website. Without knowing how to create grids how can we achieve that? Without knowing the innerworkings of a grid. Without knowing what a grid actually does. Without knowing how to position elemets and align them through grids how can we efficiently create a simple website. Now I am trying to create smells like bakin' from my memory after watching and following along the video. However, I don't know which grid_(number) does what. If I knew how to create my own grids, would have known where to use which grid. However, now I am bound to follow the tutorial blindly without understanding which grid does what? How I am able to build a "simple", "very simple" website on my own. Please Help! And I suggest to add a comprehensive section on grids in css deep dive.