It is our new, currently developing feature of auto generated guitar fingering. It can generate finger placements for almost every tab.
However there are some drawbacks, that is why it is in a beta state at the moment. The algorithm can be a little wrong sometimes and not be able to define what fingers to put on certain intervals or notes. But you still should give it a chance :)
Please feel free to report any mistakes in the feature, your opinion about them, and other ideas to our email support+web@songsterr.com., or use the feedback box down below.