The following will happen at the backend
1.) Notifies the primary database that a switchover is about to occur
2.) Disconnect all users from the primary database
3.) Generate a special redo record that signals the End of Redo (EOR)
4.) Converts the primary database into a standby database
5.) Once the standby database applies the final EOR record, guaranteeing that no data loss has been lost, converts the standby database into the primary database.
The new standby database (old primary) starts to receive the redo records and continues process until we switch back again. It is important to remember that both databases receive the EOR record so both databases know the next redo that will be received.