CEL means some sensor or other somewhere has reported an odd reading. It may or may not relate to anything or everything. Reading the codes will accurately tell you what system reported the error, but it will not necessarily tell you what is wrong. And it can range from gas cap is loose to engine just fell out on the street. It may or may not be related to overdue maintenance issues.
Sometimes all you need to do is clear the code. Sometimes the code will clear itself after 3 or 4 (or maybe 10) restarts. But in any case, reading the code is the necessary first step.