Accounts
Apps can work without accounts, with optional accounts, or with required sign-in. With optional accounts, people can browse first and sign in when they want to save something. Ask for it in chat: "People sign in to book" or "Everyone must sign in".
App users sign up with an email and a password. There is no email sending, so there are no reset emails. If someone forgets their password, set a new one for them in the Users tab.
Who sees which records
Each kind of record has one rule. Private records are seen only by the person who made them, like a diary. Shared records are seen by everyone signed in, like a family journal. Public records are seen by anyone, even without an account.
Managed records are seen by the person who made them and by your staff, like bookings or support requests. Staff-edited records, like a class timetable, are seen by everyone and changed only by staff.
Say what you want in plain words. "Only the person who posted can delete it" or "Customers see only their own bookings" is enough.
The Users tab
The Users tab lists everyone who created an account in the app. You can set a new password, sign someone out on all devices, or disable an account. A disabled user is treated as signed out.