The fuel systems on newer vehicles are closed systems. In that I mean that they are supposed to be air tight to prevent gas vapors from escaping into the atmosphere. If your trouble codes are saying tighten you gas cap, that means the computer is detecting an air leak in the system. You should tighten your cap till you hear 2-3 clicks from the cap. If you still get the condition after that, your cap may be defective. You can replace it if needed. If it still throws that trouble code then there is some other air leak in the system. It really isn't a major problem. Some claim it can effect fuel mileage but that is somewhat dubious. It probably has only a minimal effect. But it is worth checking out.
This could mean your gas cap needs tightening. You can check to make sure that it is securely tightened. If you have already checked it and it seems secure, it could mean that the cap is defective. If it appears tightened and the message is still on, then I recommend you take it to the dealer to have them check the cap.
Yukong is right. I have driven for years with the same trouble code on my car and it affects nothing. As long as your vehicle is out of warranty, and you don't have to pass a state inspection there is no problem.
A new gas cap is under $ 10.00 at any auto parts stores for your vehicle and if that does not fix it, it could be a bad sensor. Autozone and other auto parts stores will clear out error codes from your computer and read them for you for free.
It could be, after changing out your gas cap that you just need the codes cleared and all will be well.