Use rs_init to add the standby database and its RepAgent to the replication system, then you initialize the standby database with data from the active database.
After you add the standby database to the replication system, you must prepare it for operation.
You can then enable replication for objects in the standby database and grant permissions to the maintenance user in the standby database. Whether or not you need to perform these steps depends on your method for initializing the standby database.