Sheila

I have a Nikon D80 I have very little knowledge about the camera, I used it for a while in auto but have started trying it in manual,I have got a few good photos but I don't have a clue how I achieved them now I can't get a clear photo even when I put it back in auto!!!!!! what have I done to it can......anyone help it's getting me so frustrated i have been trying for a few days now....am thinking of going back to my little aim and shoot camera