Settings (main menu) is where you manage your own login and, as an account administrator, the account itself: its details, subscription, invoices, venues and users. It also switches the app between dark mode and light mode, sets the language of the app, and lets you review the app.
Which items you see depends on your permissions. Everyone sees Your login. Account and Users need the Admin permission on the account, and Venues appears when you have the Admin permission on the account or on at least one venue. Learn more about Permissions.