Matriculation is a noun meaning admission to a group, particularly a school. Matriculation is what hopefully follows after you send in your application.
Though the dictionary sense of matriculation is admission, in practical use matriculation takes place when you enroll at a school. In other words, you can’t just be accepted to complete matriculation; you have to have to enroll, register, and matriculate. If you get a letter from a college or school with a list of what to do before your matriculation, those are the things you need to do before you arrive on campus — like send a big check!