When you restore a database instance, you restore it to the last consistent state it was in before a system failure (such as a damaged hard disk). To do this, you need seamless data backups and log backups.
You can also restore a database instance to a state it was in at a point in time in the past.
Concepts of the Database System, Restoring the Database Instance
Database Manager GUI, Restoring Data
Database Manager CLI, recover_start