Seven steps to creating a catalog database

The catalog database is used by RMAN to store historical information on what was backed up, when it was backed up, and where it was backed up to. This information is used to restore and recover a database using RMAN. The target database is the database that you are backing up and restoring. When you start a RMAN session, you can connect to the target database and optionally, the catalog. It is very good practice to make the Recovery Catalog in a completely separate database on a completely separate server. Creating the catalog is quite easy. You follow these simple steps:

1) Find a database on a server separate from the target database. If you don't have such a database, you will have to create one.
2) Create a user in this database and make sure it can create tables in a tablespace in that database. You can call this user anything you want. In my environment, I made things easy and called this user 'rman'.
3) Grant the RECOVERY_CATALOG_OWNER role to this user.
4) Fire up RMAN at the command prompt.
5) Issue the command to connect to the target database.
6) Issue the command to connect to the catalog database using the user you created in step #2.
7) Issue "CREATE CATALOG;" to create the Recovery Catalog in the catalog database.

All of these steps are fully documented in the Oracle RMAN documentation. I highly recommend reading it as RMAN is a little complex and takes a while getting used to it.