Get a OBDII reader, either an attachment that uses your cell phone or a standalone reader that will tell you what the code means. From there it all depends on how mechanically minded you are. Most issues with common engines can be solved by Googling the problem.
Case in point: Peggy's SportTrac CEL came on, and the check showed "Lean Bank 1" and "Lean Bank 2". Plug those into Google and it came up with several possibilities. One was a vacuum leak, caused by a hole developing in a rubber hose elbow. It was impossible to see easily, but it was there and the repair part from Ford was about $75. Thanks to Google and a very small amount of digging, the rubber elbow was replaced with a $1 elbow from AutoZone. Reset the code and all was well.
Google and YouTube can be your friend with things like this.