Following are the minimum steps to a hot backup:

1) Make sure the database is in ARCHIVELOG mode.

2) Prepare the database for a hot backup:
SQL> ALTER TABLESPACE tablespace_name BEGIN BACKUP;

3) Obtain the oldest online log sequence #:
SQL> ARCHIVE LOG LIST;

4) Back up the database using a system command:
UNIX: obackup, tar, dd, etc...
NT: backup manager, etc..

5) Set the tablespace to no hot backup mode:
SQL> ALTER TABLESPACE tablespace_name END BACKUP;

6) Obtain the current online log sequence #:
SQL> ARCHIVE LOG LIST;

7) Force a log switch:
SQL> ALTER SYSTEM SWITCH LOGFILE;


Good luck
R