Fuel 2001 Mustang - Check Gas Cap Light Problem

(2001 GT AUTOMATIC) So a while back, when driving i noticed my "check gas cap" light came on the dash on the opposite side of where the check engine light is. Well i kinda figured it didnt mean anything as far as a damper to performance. I ignored it but later i decided to buy a new gas cap to get rid of the light. Well it went away but it came back a few days later ALONG with an engine code that said i had a NON gross evap leak. What could this mean? Do i have an evap leak unrelated to the gas cap or is this related? And what else could i check?

Is it hard to do by yourself? Im trying to familiarize myself with all the parts and areas to check. I noticed that the canister on the driver side next to the gas tank is probably where the leak is because i got in a wreck and thats where the car was struck