The check engine light is on because there is an error code stored in the computer that runs the engine. The first thing you need to do is find out what that code is. Take the car over to a national chain auto parts store (like AutoZone) and most of them will read the code off of the computer for free.
When you get the code, come back here, and in "Additional Details" put in what the code is. That will help me, or anyone else who wants to answer your question, determine what the problem is.