Typically you set up the SQL server maintenance jobs to dump backups into the backup directory and then you use backup software to back up this backup directory. Otherwise you use software specifically designed to back up SQL like Tivoli Storage Manager tdpsql.
All backup software (including SQL Server backup software and backup agents like Tivoli, CommVault, etc) use the BACKUP DATABASE command to backup the database to either disk or tape. You can manually run the command as needed, or schedule it via a SQL Agent job, or use another scheduler. You can also use the maintenance plans to control the database backup.