Troubleshooting engine problems begins with diagnostics:
Vehicles 1996 and newer have an OBD-II port that can be used to read/reset codes and read outputs from sensors . The port is usually under the dash.
OBD-II scanners have gotten progressively cheaper and are now available in bluetooth/wifi models that communicate with and display on your smartphone and tablet. They are generally less than $20.
Once you have the CEL code you can google it or check it against published lists of codes for your vehicle's make:
In forums you may see the acronyms DTC (Diagnostic Trouble Code) or CEL (Check Engine Light) referring to codes readable by a OBD-II scanner.