If you are sure of good battery and clean connections: Use a jumper cable. Place one end directly on the starter terminal. Turn the key on. Take the other end of the jumper cable and go directly to the positive battery terminal. If the car starts you have a good starter, but a bad solenoid. Replace solenoid. If it won't start, replace starter. BE CAREFUL ! You can figure this out with a volt/ohm meter also, but it requires a meter and a little more know how.