I know about visibility, but that was not what i was asking.
my question meant that in the same form where users register can i make a specific entry (in a form) relays on another entry (in the same form) ?
or i would have to divide them into two forms to make it easier ?
Yes, you would use visibility to achieve this. A way to display an input if user made certain choice.
If user is a teacher than show button Teachers-room, if student show (instead) button Classmates…etc…