P0456 (M) Evap Leak Monitor Small Leak Detected Leak has been detected in the evaporative system.

I am new to the board and looking for a little help. I just purchased an 02 Durango, and the check engine light came on after a couple of days. I checked it and found this code in the odometer. I don't know a hole lot about vehicles, and was wondering what this was, if it is serious, and if I need to take it in. Any help would be appreciated. Thanks.

 

Check you gas cap. Make sure it is tight.