Apart from performing consistency checks on a database, DBCC CHECKDB can perform repairs of the majority of corruptions that it finds. I say "majority" and not "all" because there are some corruptions that DBCC CHECKDB cannot repair. This list includes:
Corruption in the leaf level of a critical system catalog clustered index
Corruption in a PFS page header
Data purity errors (error 2570)
Errors from system catalog cross-checks (error 8992)
If any of these corruptions are present, DBCC CHECKDB repairs as much as it can and indicates which corruptions cannot be repaired with a 2540 error ("The system cannot self repair this error").
This book is not the place to discuss when repair should be used, but suffice it to say that restoring ...