If it is clicking, the solenoid is engaging but the motor itself is not turning. There are two reasons for this:

Either there is no power to the starter, or the starter motor isn't working.

The starter is connected to the battery via a thick lead from the battery +ve to the large terminal on the starter, and a thick lead from the battery negative to one of the bolts which hold the starter in the block.

Check these connections are good and tight, and that your battery is charged. If it is, the starter is knackered.

Rick