1999 Chevrolet Camaro wont start

Have the battery's state of charge checked at an auto parts stroe which will check and/or charge it for FREE.
Once the battery is deemed good, reinstall it and try starting it again.
Also, while the battery is out, check the starter bolts to be sure that they are tight.
Post the results here.

OK. Try this:
1. Turn the headlights on bright.
2. Have an assistant to try to crank the engine while you watch the headlights to see if (1) they go out or (2) dim severely or (3) remain bright.
3. If they go out, the battery is weak or the cable ends are dirty [this is the end at the battery, the starter, and the ground at the other end of the NEG cable. Or the starter is faulty.
4. If they dim severely (same as #3)
5. If they remain bright, you have a loose [bad] connection at one end of the battery cables unbolt the cables and clean the cable end and mounting surfaces.

Post your results here.

As a last resort; you'll have to try and turn the engine over by hand. To do this you'll need a breaker bar [aka pull-handle, cheater bar, etc] and a socket that fits the center crankshaft pulley bolt. Put the socket and pull handle on the bolt and turn the engine in the direction which would tighten the bolt. Be sure to rotate the engine two complete revolutions. You can try rotating it in the others direction [it should go that way as well]. However, if the bolt starts to uncsrew tighten it back up and just be satisfied that it turned in the other direction - that was good enough).
If you can turn the engine by hand, the starter should be able to turn it easily.

Now, If all that is done and it still will not spin over; a faulty starter is the likely suspect. You'll have to remove it to have it tested (but only is necessary).

A breaker bar/pull handle is just a long, strong socket wrench made to loosen large bolts. They can show you one at the auto parts store or you can see it online.

DO NOT buy a carburetor. The carburetor has nothing to do with the ability of the engine to spin over. You may need one eventually, but until you get the engine running you can't accruately check the carburetor.

Please try the tests I've outlined in the previous post. These tests are not to check the lights, but to check starter amperage draw and battery efficiency without using a gauge or meter (the way to do it in your yard without taking it to the shop). Once these tests are complete, post the results here.

However, if you have more time than tools, you can remove the starter and have it tested for FREE at the autoparts store.

It is important to see if you can turn the engine by hand. The engine may be locked up from back when it was being driven - this may be the reason it was not being used for so long.