Starting data guard services is actually a reverse process of stopping data guard services by any ways. Let's see how we start the services along the same route of stopping.
With the broker
If you've ever disabled the configuration, you should enable it back before doing the rest of steps.
DGMGRL> ENABLE CONFIGURATION;
Enable Apply Service
We start the applying service on the standby database.
DGMGRL> EDIT DATABASE 'standby_db' SET STATE='APPLY-ON';
Enable Transport Service
We start redo transport service on the primary database.
DGMGRL> EDIT DATABASE 'primary_db' SET STATE='TRANSPORT-ON';
Without the broker
Start recover managed standby database in the standby database.
SQL> alter database recover managed standby database disconnect from session;
Start transport service by enabling the log destination in the primary database.
SQL> alter system set log_archive_dest_state_2=ENABLE sid='*' scope=both;
Please note that, stopping data guard with or without broker is just a reverse process of starting data guard.