What is the use of SCN number? When does SCN increment?

The SCN is an important quantifier that oracle uses to keep track of its state at any given point in time. The SCN is used to keep track of all changes within the database, its a logical timestamp that is used by oracle to order events that have occurred within the database. SCNs are increasing sequence numbers and are used in redo logs to confirm that transactions have been committed, all SCNs are unique. SCNs are used in crash recovery as the control maintains a SCN for each data file, if the data files are out of sync after a crash oracle can reapply the redo log information to bring the database backup to the point of the crash. You can even take the database back in time to a specific SCN number (or point in time).