Almost every app will have an option for participants to register to participate in the event. Registration workflows are mostly autonomous. Data is stored locally automatically and will remain on the device until it is synced.
Events that allow preregistration normally contain a check-in option. This is a section on the first page of the workflow allowing guests to enter their name to search for their information. Upon selecting their name it will walk them through the rest of the experience with all their information from the RSVP site pre-entered.
A guest may also have a QR code from their RSVP entry. This code can be scanned by selecting the Scan option on the first page. Once scanned the workflow proceeds as normal with information populated from the preregistration.