Snowbum has a tutorial on drilling mufflers for a better sound, and this "deep drill" is part of it. Can't find the link, but if you Google Snowbum, you'll easily find all his detailed articles.
Sadly, if you require pictures to understand instructions (vice words), Snowbum is not the guy for you. Fortunately, he uses many nice bright colors, sorta like Crayons, which helps when reading his long and quite specific instructions. He usually repeats the IMPORTANT stuff at least twice, a feature of his work that I appreciate.
Being a "non-trained" wrench, I read EVERYTHING I can get my hands on before I even think of doing a new job, but that's a personal thing. What I do next is READ EVERYTHING again. Then, after that, especially if I haven't done the job before -- I READ EVERYTHING again, and I'm not kidding. Yes, I'm old, but you may be surprised at all the details that you missed the on the first (or even second) reading. When I follow this discipline, I usually don't have parts left over after re-assembly -- and I take that for a good sign.