The flaps can jam for a variety of reasons:
Computer that drives the flaps has failed
Lever that selects the flaps has failed
System has detected a flap asymetry and has locked the flaps in place
Flap mechanism has jammed
Hydraulics that move the flaps are faulty
Depending on the reason Ecam will ask for the lever to be recycled or not. Either way first action is to select the speed to avoid a flap overspeed, after that there is no hurry, get to a safe altitude and location then go through the Ecam followed by the QRH.