I agree that an FW is probably not a good candidate for FMQing, although I think some people here use them for that purpose. Aside from the motor not being that strong, the space underneath the arm is very small.
Looking at your photo, the large slot is where you insert the screw through the cover and then screw it into an available hole on your machine. The small slot is where the needle goes. I would say position the piece so that the needle goes through the small slot, then look for a screwhole in the bed of the machine to position the large slot.
According to your photo, the cover piece is turned the opposite way of how it would actually be used (180 degree turn).