How to create RMAN catalog

1. Create a recovery catalog database with DBCA called RMANCAT.

2. Start SQL*Plus and connect as a user with administrator privileges to the database containing the recovery catalog. For example, enter:

$ sqlplus SYS/pass@rcat AS SYSDBA

3. Create a tablespace for the recovery catalog. For example, enter:

SQL> CREATE TABLESPACE catalog_tbs DATAFILE '/u01/app/oracle/oradata/RMANCAT/catalog_tbs_01.dbf' SIZE 1024M AUTOEXTEND ON NEXT 5M EXTENT MANAGEMENT LOCAL SEGMENT SPACE MANAGEMENT AUTO;

4. Create a user and schema for the recovery catalog. For example, enter:

SQL> CREATE USER rman IDENTIFIED BY rman DEFAULT TABLESPACE catalog_tbs QUOTA UNLIMITED ON catalog_tbs;

5. Grant the recovery_catalog_owner role to the user. This role provides all of the privileges required to maintain and query the recovery catalog:

SQL> GRANT recovery_catalog_owner TO rman;

SQL> Grant connect, resource to rman;

Once the owner user is created, the RMAN recovery catalog schema can be added:

6. Connect to the database that contains the catalog owner. For example, using the RMAN user from the above example, enter the following from the operating system command line.  The use of the CATALOG keyword tells Oracle this database contains the repository:

C:\> rman catalog rman/rman@rmancat

7. Now, the CREATE CATALOG command can be run to create the catalog. The creation of the catalog may take several minutes.

RMAN> create catalog;

While the RMAN catalog can be created and used from either a 9i or 10g database, the Enterprise Manager Grid Control database must be a 9i database.  This is true at least for release 1, although this may change with future releases.

Each database that the catalog will track must be registered.
Registering a Database with RMAN
The following process can be used to register a database with RMAN:

1. Make sure the recovery catalog database is open.
2. Connect RMAN to both the target database and recovery catalog database. For example, with a catalog database of RMANCAT and user RMAN, owner of the catalog schema, and the target database, SME, which is the database to be backed up, database user SYS would issue:

$ rman target / catalog rman/rman@rmancat

3. Once connected, if the target database is not mounted, it should be opened or mounted:

RMAN> STARTUP;
--or--
RMAN> STARTUP MOUNT;
4. If this target database has not been registered, it should be registered it in the connected recovery catalog:

RMAN> register database;

The database can now be operated on using the RMAN utility.

RMAN Compatibility Matrix
In general, the rules of RMAN compatibility are as follows:
•    You can create an 8.x or 9.x recovery catalog schema in any Oracle database release 8.1.x (or higher), and a 10.0.1 (or higher) recovery catalog schema in any Oracle database release 9.0.1 (or higher).
•    The recovery catalog schema version must be greater than or equal to the RMAN client version.
•    If the recovery catalog is a virtual private catalog, then the RMAN client connecting to it must be at patch level 10.1.0.6 or 10.2.0.3. Oracle9i RMAN clients cannot connect to a virtual private catalog. This version restriction does not affect RMAN client connections to an Oracle Database 11g base recovery catalog, even if the base catalog has virtual private catalog users.
•    Ideally, the versions of the RMAN client and the target database are the same (although there are other valid combinations, listed in Table B-2). The RMAN client cannot be a greater version than the target or auxiliary database.
•    While backing up an Oracle Database 10g or later database with the Oracle9i RMAN client, you cannot include a control file that was created using COMPATIBLE=10.0.0 in a datafile backup set. The workaround is to turn control file autobackup ON.
•    The version of an auxiliary database instance must be equal to the version of the RMAN client.
•    Any release of Oracle database can restore backup sets and copies created by any prior release back to Oracle8i.
Table B-2 shows version requirements for RMAN components. Note that the symbol >= before a release means all Oracle Database releases from this release or later along with their patches.
Table B-2 RMAN Compatibility Table
Target/Auxiliary Database    RMAN client    Recovery Catalog Database    Recovery Catalog Schema
8.0.6    8.0.6    >=8.1.7    >=8.0.6
8.1.7    8.0.6.1    >=8.1.7    >=8.1.7
8.1.7    8.1.7    >=8.1.7    >=RMAN client
8.1.7.4    8.1.7.4    >=8.1.7    8.1.7.4
8.1.7.4    8.1.7.4    >=8.1.7    >= 9.0.1.4
9.0.1    9.0.1    >=8.1.7    >= RMAN client
9.2.0    >=9.0.1.3 and <= target database executable    >=8.1.7    >= RMAN client
10.1.0    >=9.0.1.3 and <= target database executable    >=9.0.1    >= RMAN client
10.2.0    >=9.0.1.3 and <= target database executable    >=9.0.1    >= RMAN client
11.1.0    >=9.0.1.3 and <= target database executable    >=10.2.0.3    >= RMAN client
11.2.0    >=9.0.1.3 and <= target database executable    >=10.2.0.3    >= RMAN client

When using an older version of the RMAN client with a newer version of the database, you do not get the features of the newer version. For example, when using the Oracle9i RMAN client to back up an Oracle Release 10g database, you do not have access to features like the fast recovery area, flashback database, TSPITR with an RMAN-managed auxiliary instance, or recovery through RESETLOGS.
Matrix refer by
http://download.oracle.com/docs/cd/E11882_01/backup.112/e10643/compat003.htm