I don't understand what it does
Flagged to move to the proper forum (this one is for 3rd party products, the Inquisitor is a Paizo class).
And it's fairly simple. You spend a Swift action to gives your weapon the Bane special weapon quality against a type of your choice. This lasts up to number or rounds equal to your level, which you can end at any time.
So a 10th level Inquisitor who's fighting a Dragon can activate his Bane ability to get +2 to-hit and 2d6+2 damage (and increased DR penetrating ability) against Dragons only. The fight lasts 4 rounds. The Inquisitor still has a total of 6 rounds he can use that day.
At 12th level, Greater Bane simply increases the bonus dice from 2d6 to 4d6.