I didn't go to Mazzoni, but the clinic I go to in DC is very similar. My first visit was mostly my doctor going over my medical history, talking about what T could/would/might/won't do for me, and getting a consent form to read over at home. They also required blood work to be done while fasting, so check and see if you're allowed to eat/drink before. I was not and my appointment wasn't until nearly lunch time. Kind of miserable, but worth it.
I had another appointment 3 weeks later where I officially got my prescription. If I hadn't started around the holidays, I probably could've gone back in a week later (they get booked up very quickly around the end of the year).