GM-GMC: my car, positive cable, chevy

Question
I have a chevy and it won't start.I thought it was starter and took it off and it tested good.I put it back on and started to hook up positive cable without key in car.It started sparking what is wrong.

Answer
I would recommend disconnecting your battery before trying to reconnect the starter.  Ensure the wires are installed in the correct places and you should be good.  It isn't abnormal for a wire to spark when installed if the battery is hooked up, but it not a recommended practice.
Hope this helps