The first section How Backup Works, covers each of the types of backup explains how each one works and gives some ideas on how each can be used to back up a database. This chapter concentrates on the Transact-SQL syntax for performing backups. This section covers the backup process at a very low level. It doesn't really delve into when backups should be done. Takes all the pages that are in use in the database and writes them to specified backup media.
Transaction log backups.
Takes all the pages in the transaction log and writes them to the specified backup media. Takes all of the pages that have changed since the last full database backup and writes them to the specified backup media. Takes all the pages present in the specified file or file group and writes them to the specified backup media. This is great for backing up huge databases. Most of the backup commands require that a backup device be specified as the destination for the backup.