A new version of TinyUmbrella is now available, it adds iOS 6.1.1 support for the iPhone 4S.
TinyUmbrella is a tool that gives users the ability to back up their SHSH blobs. In English, that means users can keep those backups so that they can downgrade back to an older version of iOS even after Apple has moved on to a new one and stopped signing that firmware file (Normally, it wouldn’t be possible to revert to an older version of iOS because of a system that Apple implements.)
Jailbreakers are always advised to make such backups. While it’s not a necessity, it’s a good idea to do it, and it can be a lifesaver later.
You can download TinyUmbrella here, at the official website.