Well, running more off of RWBY weapon logic than real weapon logic.

Staff mode is activated by slamming the flat of the blades together and pulling the handles in opposite directions. As this happens a dust charge is activated and the blades kind of spiral as they extend. 

The end result is a metal coil around a nasty elemental center, probably fire or lightning. Said element is channeled into whatever gets hit while your character wears special gloves to avoid being damaged himself.