I'm new here so I apologize if this is placed in the wrong section. I tried searching for the answer I'm looking for but sadly cannot find any help

I'm currently in college and one of the courses I'm taking at the moment is for 3D modeling. We are using Maya, of course. I'm having a lot of trouble with my professor as he explains how to model very quickly and I cannot keep up. He also tends to teach methods that are different from others who post tutorials on the internet. So here is what I need help with:
I need to know how to model a door frame/insert for the door that will be on my building/house that we are creating for my midterm. Basically what he wants us to do is to select the faces of the doorway we created, invert the selection, delete, and use that as the basic outline of the door frame. Then, after we have removed any edge loops on it, we are to extrude out the sides and then extrude inside of it to make a "flange" as he called it. Then he did all kinds of splitting, merging, and just sooooo much technical work compared to how everyone else models it. So, i'm completely lost! I'll upload screenshots of how he did it.
I'm sure this is very simple and i'm just making it harder than it needs to be. I'm just having a hard time getting it to extrude the way he has it and all of my notes aren't making sense
