generate mesh on colliders

hello guys I'm a beginner at unity, I was able to do the first few steps of this video [https://youtu.be/Psq8rICishw] but I was stuck at 2:31 , the part were you generate a cylindrical mesh around the colliders. I know it sounds stupid but I just don't understand the terms he is saying like how do you add another set of vertices from top to bottom etc. Perhaps someone could explain it in a noob friendly way? thanks!