When you try to start your car it makes a clicking noise?

When you try to start your car it makes a clicking noise?
the most common cause is the battery is not sufficiently charged (has been drained by something that stayed on in the vehicle or the car has just sat for too long). Jumper cables or a jumper box usually helps this, if the battery hasnt gone bad.
another culprit is dirty or corroded connections between the battery and starter.

and it can also be the starter itself has went bad if there is 12-14 volts from the battery and good conductivity all the way to the starter.

and the least common (and most expensive): the engine could be locked up. this is fairly easy to check for though as most engines can be turned either by hand or a socket on the pulley at the bottom of the serpentine or v-belts to see if it is seized up. But i would start with the aforementioned electrical things as those are alot more common