If you can hear the starter soloid click when you turn the key or press the start button it means that keyswitch is working and has power to it. You can also be reasonably certain the solenoid itself is working, although making a clicking sound is not a 100% guarantee of that.

The starter motor spins but doesn't turn the flywheel

The starter motor spins but the engine doesn't turn over.

The starter motor doesn't spin when but the solenoid clicks

This topic covers the situation where you turn the key on your boat and the starter motor doesn't spin but you can hear the solenoid clicking.