My car wants to start but won't

Spark plug/battery/batter plus and minus cables,

This is probably either your started or your battery. The clicking sound is your starter trying to turn the motor over, If you can, test the battery with a battery tester, they are pretty cheap, or you should be able to take the battery out and take it to your local auto-parts store and have them test it for you, if the battery is good than its probably your starter as long as you are getting fuel, If you can't test your battery find someone to jump start the car, if that doesn't work it means it is not your battery. Spark plugs are usually durable and last a long time especially the iridium spark plugs that are factory for Grand Prix's , that's why I would start with the battery and starter, just a warning don't jump start the car for too long if your battery is good it could hurt the electrical system in the car, also these batteries can be a little difficult to get in and out.

And make sure the battery cables are tight to the battery. If you can move them at all tighten them before you do anything. After that have the battery load tested as has been suggested. Starter is unlikely if its making that clicking sound although it is a possibility. have it tested first before you buy a new one though. They're not cheap and don't often fail. It's definitely not spark plugs.

Battery is nowhere near enough for that car. Need at least 650 CCA and 800 to 950 ca

Starter may be done now too

It's been 8 months. I'm guessing he's got it sorted out by now.