First thing you can do is check the gas cap, if it is loose or off this will turn on this light. If it's OK, then you'll need to have the diagnostic trouble codes checked, there is going to be one or more stored in the engine control module. There are hundreds, so it's not very useful to speculate about why the light is on. You can get the codes read out for free at some parts stores, and post the codes here and we can give you some better information about what is happening. Whatever you do, don't let the parts employees tell you what you should replace, they are not technicians and are trying to sell parts.