Freeze plug location 01 sunfire gt 2.4L - 2001 Pontiac Sunfire

They are all around the engine, 2 or 3 on each side (front wheel drive cars like yours the engine is sitting sideways) and sometimes one on the end but usually have to take the transmission off to access that one, they are just silver (if not rusted up) plugs that get tapped into the engine, to get them out just tap on one edge until it flips sideways and grab it with pliers or get screwdriver behind it. try not to let it fall inside the engine. Generally they are called frost plugs and they are to protect your engine from cracking in case water freezes inside of it but if you have good strong anti-freeze (glycol) in your rad that shouldnt' be an issue but worse than the frost plug popping out is cracking the radiator due to insufficient strength of your anti-freeze.\
A lot of cars now may have a block heater and this is inserted into a frost plug once removed and a bolt tightened, this is the weakest link usually and may leak, sometimes can be tightened but a block heater could be where your issue lies.