I would like to know if it is possible to create an app that allows the users to take a cite.
Hmm, I don't understand, try to explain in more detail
I would like create an application that allows the user to book an appointment, that is, a day and an hour in which we can meed each other, do you understand me?
This tutorial describes a way to book a room, that is something similar to what you describe Judit:
Perhaps you can adapt it to your purposes?