Just bought a 2004 Pontiac grand prix gt started off good then just notice it is saying overheating put antifreeze in it and oil does look really black looking this is my first car

The fact that Pontiac's are no longer made is not an issue. I am still able to find parts for my Pontiac Astre which turns 40 this year. And other GM cars have the same engines. While walking away is sometimes best, that may not be the case just because of a couple of problems. If you bought it at a buy here pay here lot, it probably is a piece of junk. And I would take it right back to them. If you have paid for it already, you need to decide if fixing the problems it has are worth it, or if you need to take it to a junkyard which would likely give you about $200. As far as black oil, change it or have it done. As long as the oil is not creamy or white looking you are probably OK. As far as the overheating, this can be very serious and can destroy an engine very quickly. There are many simply fixed potential causes including, thermostat, clogged radiator, bad hoses, worn out water pump, or engine timing. If it needs coolant again soon, I would look for a leak, and keep an eye on the temperature gauge or dash light. Never open the radiator when the car is hot! Wait for it to cool down first. If you know someone who can help you out, ask them to look it over. Or, have it assessed by a professional mechanic. It may be expensive, but they can give you an idea of what you are getting in to. First cars are tough, be smart and educate yourself. Google for info, and youtube has videos that may help you learn how to do simple things. Good luck.

The fact that Pontiacs are no longer being produced is neither here nor there. The fact that the oil is really black is no big deal either. If anything it is an indication that all is well inside the engine, for now at least. If it were some other color than black then I would be worried. If you don't know when it last had an oil change it may well be time for one in the near future, but its not an emergency. You can expect the new oil to become black fairly soon as well. No big deal. However, fix the overheating problem first. There's no point wasting money on oil and filter if the engine has some terminal problem, which it probably doesn't. Make sure the cooling system is full and has no air trapped in it, which is very common. There is a bleeder valve near the thermostat, or have a shop pressure test the system and make sure it is full and the thermostat is working. That will likely fix it. If the coolant level keeps going down you have a leak. If its a minor leak it can likely be fixed with a cooling system additive like Bars Leak. It is very effective and does not hurt the car in any way. If it is a major leak that leaves puddles of coolant under the car then you have some work ahead you (or some major expenses) changing failed manifold or head gaskets. Good luck with your car, let the learning begin.