But if you want to go to the top, here's how it works. Face the tower entrance. Then turn to your right. You'll see a building down the path on the left. In there is the ticket booth. The church is free to visit, but you still need a ticket. At the ticket booth, let them know which buildings you want to visit (the church, the bell tower, the baptistery, monumental cemetery, the Opera Museum, and the Sinopie Museum). There are guards at every entrance. They scan your tickets, so no cheating and marking off extra monuments on your ticket.
Your tower ticket is good for a specific time, so make sure you're in line and ready. We held our friends' bags for them because they don't allow bags or containers in the tower. You can check your things in the cloakroom if you don't have anyone to hold your things for you.
I think I said this last time, but Pisa is good for a pit stop to see the Leaning Tower and maybe the nearby buildings. It's not really a destination spot. We stayed at Camp Darby so we drove down, checked in, went to see the tower, came back, and relaxed the rest of the night to be refreshed for Florence the next day.