Database Backup for data and log files
Don't worry about extents and pages.

A Full backup contains all the data pages.  The pages are not written to the backup at a single point-in-time.  So a Full also contains the log records needed to redo/undo the changes from the earliest page to latest transaction committed during the backup.

A differential backup omits all pages not changed since the last Full backup.

A log backup contains all log records since the last log backup.