1992 Geo Storm car idles and then turns off

My problem begun just yesterday at wells fargo's parking lot. I jumped in my car and I turned it on and it made a loud popping sound and after that it began to sound as if the engine was knocking. I immediately shut it off and tried turning it on again. It kept knocking so I left it there. I came back later after some advice and looked under the hood and one of the spark plugs was hanging out so I put it back in and tightened the rest of them. My car was also low on engine coolant so I refilled it up. It was overheating like 3 days before this incident. I turned on the car and the engine sounded fine, but now it would idle at 2000 rpms and then it would choke and die. I tried driving it home like that and when I gave it gas it would respond but then it would go down in rpms so I would have to gas it again. After the engine was on for a while it quit dying on me. It was driving just fine. So I am not sure what exactly is going on. Oh yeah the oil condition is just fine. I am confused. I am thinking of taking it into a shop but my budget is very small.