2002 Pontiac firebird starts occasionall. Changed batterie checked starter... Security light come on occasionally. Fuels good, hear fuel pump. Anything???

yes...um...the main battery cable from the negative terminal should be connected to the motor block...near the alternator....be sure the block has this ground strap~...also the main ground to frame connection should be wirebrushed free of corrosion~

Alright the cars my brothers who not one to get in there and try to figure it out. So I just heard that he's actually been able to start right after he turns engine off. Last couple times I've tried it would never start back to back. Or it seems like the engine won't crank when hot. Where should I start?

Is the ignition switch bad?...I'd test this one to make sure the contacts are good...if it's like you said....off means still on~ https://www.google.com/#q=2002+Pontiac+firebird+ignition+switch

Assure the main ground connection 1/0 cable from the battery to the ground is corrosion free....wirebrush the lug and place where it bolts to...to assure a full 300 cold cranking amp potential~

another goodie is the ignition relay~~~ https://www.google.com/#q=2002+Pontiac+firebird+ignition+relay

sound like you have a starter going bad... hope this helps and don't confuse you like other answers on the site can.. lol