The switch
Open Booking Page. The status card at the top shows whether your page is live, and it is the only place the page is turned on or off.
While it is off
Your link does not show a booking page, so nobody can book online. Existing appointments are untouched — your calendar, customers and notifications keep working normally.
When to turn it off
While you are still setting up, during an extended closure, or if you want to stop taking new online bookings for a while. To close only certain days, block that time under Schedule → Availability instead of turning the whole page off.