Unfortunately, not every place treats it the same way so it's confusing.

Most places I've gotten the service charge details from share the service charge somehow across the staff. It varies from place to place how the split is calculated.

I don't know of any places that give the service charge 100% to the server so I'll typically add a little. At least enough to bring it up to 20 or 25%. I give the extra in cash if I can unless I know the restaurant allows the server take extra credit card tips out of the drawer at the end of the day.

Some places take the service charge AND any cash/credit card tips and gross the server's pay up BUT only to a max of $10/hr. The rest gets spread across the staff in the same manner and then I guess the house gets the rest.