Other than the few operations that can be minimally logged (see Books Online, Operations that can be minimally logged), it fully logs everything. So most inserts, all updates, all deletes are fully logged. Schema changes are logged (depending what they do how much is logged for each).
Enough information is stored for the DB engine to be able to undo or redo any operation.
If you're curious...
select * from fn_dblog(null, null)
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)SQL In The Wild
: Discussions on DB performance with occasional diversions into recoverability
We walk in the dark places no others will enter
We stand on the bridge and no one may pass