What transaction logs are for I'm confused about tranasaction logs for SQL Server. I was under the impression they can be used to roll the database forward. For example say I made a software release on Sunday, I added three new columns. But four days down the line we discover a bug, could I roll the database back to the Sunday's backup before I did the release and then use the transaction logs to insert any data that's been inserted since Sunday?
Yes, you can do what you're asking.  You should have your database in full recovery mode and then be performing log backups (via jobs/maintenance plans).

https://technet.microsoft.com/en-us/library/ms190982(v=sql.90).aspx