Head to Team → Add staff. Pick their role (Owner, Manager, Instructor, Front Desk, Sales). Enter their name and email; they get a password-reset link that sets their password on first login.
To let a staff member use the mobile app, tick "Staff app access" on their profile. Without that toggle they can still log into the web CRM but the mobile app hides staff features.
Owners always have full access. Managers see everything except billing-and-plan settings. Instructors see classes and their students. Front Desk sees the kiosk, POS and check-ins. Sales sees leads and pipelines.