transactions are logged, but each time a checkpoint occurs and the transactions are completed and written to disk, the log is truncated. You can NOT backup the log file (error). You can recovery the backup of the database, but can not do a point in time recovery – the only PIT is the time of the last backup.
Logs can grow for long-running transactions, or transactions started after the oldest open transaction.
ALTER DATABASE name SET RECOVERY FULL\SIMPLE\BULK_LOGGED.
SELECT * from sys.databases WHERE NAME = ‘name’ – view Recovery_Model_Desc.