When you execute a log backup, you use the Database Manager database tool to back up (from the log area to a data carrier) all redo log entries that the database system has written since the last log backup. Once you have backed up the redo log entries, the database system can then overwrite them in the log area.
You can also back up the redo log entries automatically (by switching the automatic log backup on/off).
Concepts of the Database System, Backing Up Log Entries
Database Manager GUI, Backup Wizard
Database Manager CLI, Backing Up and Restoring Database Instances
Database Administration in CCMS, Scheduling Log Backups