Remove the starter and take it to your local auto parts store for testing.
Bad starter, bad starter solenoid, or the problem might not be the starter at all.
either clean and tighten cable connections or get battery tested. if not the battery, it is the solenoid or the starter If it is clicking and not starting at first, but starts after a few tries, its your starter taking a dump. Replace it.
your battery is dead or the starter solenoid
Put a stethoscope or a plastic tube onto the solenoid, listen at it while a friend turns the starter. If solenoid clicks it is good. -Problem then is low battery or dud starter.
The starter solenoid is on the starter.The starter solenoid is on the starter.
I would check the starter solenoid before I investigated the starter - it's likely the cause. Have someone try starting the car hot while you measure the voltage between the starter side of the solenoid and negative - you should get battery voltage. If not, the problem is the solenoid (or somewhere before it, electrically).
The starter solenoid is part of the starter assembly so it's on the starter
The solenoid is attached to the starter. Replace the starter.
The starter solenoid is attached to the starter.
Check the starter solenoid first, followed by the starter. The starter is either not getting power from the solenoid or the starter itself is bad.
Starter solenoid sticking. Replace the solenoid if it is external. If it is internal, then just replace thee starter. It will cost a little more but you will have a new starter and solenoid.
The starter relay or solenoid is probably the problem.