My 2002 alero makes a click click sound when in the ON Position & will not start

If your battery is good, make sure the cables are clean and tight. Do that first because if its not getting a good connection thats exactly what it will act like. If not...your starter solenoid is going bad. If you get someone to try to start it while you tap the starter gently with a hammer, it might try to engage. Just dont even worry about pulling the solenoid off and only changing it out on your old starter, because a weak starter will wear out the solenoid so replace the whole unit.

Check for a good/clean connection on your battery terminals. If they have crud on them, disconnect the terminals & clean everything off with a wire brush & if possible, you can use some baking soda or even a Coke to help get the crud off. Rinse everything off & let it dry a bit (check the water level in the battery too - if the cells dry out, that'll kill it). Hook the connections back up good & tight. Then try to start the car - if that's not it. Get a jump, then go to Auto Zone, O'Reilley's, etc and get the battery & the starter checked. I'm betting it's either a poor connection, bad battery or your starter is going out. Start with your connections - that's the easy fix. Good Luck.