This image shows the main entrance to the monastery, which itself is part of a fortress. When you finally want to enter the monastery through the inner gate you will have, as is customary with Le Mont Saint-Michel, climb a very steep flight of stairs, before you meet with two guards. The visitor has to go through a metal detector, as you know it from the airport. The same procedure. For the photographer, you are not allowed to use tripods inside, flash is allowed and what they absolutely do not like is making videos. So, even if your DSLR is a perfect video cam, don't do it.
After having passed the checkpoint you arrive at the ticket counter. Entry for adults is EUR 10 each. They do have prices for children and groups. You can also book a guide to show and explain the site to you. When you go with guides you will see much more as if you go on your own; though in case you want to do your photography as you see fit, then you should plan for an extra visit with a tour guide.
The following images show a bit of the entrance section and the flight of stairs that lead up to the upper terraces from where the abbey church can be accessed.