This means that your engine management computer has detected a fault that is affecting the emissions of your vehicle, and it may or may not affect the performance of the vehicle.
You will need to have the computer scanned to read the diagnostic trouble codes that are stored, then based on the codes, a diagnostic test will need to be performed.
Check your fuel filler cap, make sure it isn't loose or left off, this will cause the light to come on. If the engine performance is poor, then you should avoid driving the car and get it checked as soon as possible, otherwise further damage can result.
You can also learn more here: http://repairpal.com/check-engine-light