A good field guide will contain keys, pictures, and descriptions of individual species. As a beginner you may choose to work through the questions in the keys or flick through the pictures to match your fungus to a photo. The best bet is probably to combine both methods. A field guide will usually only take you as far as genus with any certainty. To be sure of species you will probably still need the help of an expert, or expert advice.
It's a good idea to do most of your detective work in the field. If you do take a specimen home to identify, don't waste any time. Fungi deteriorate rapidly, and you need to examine them while they're still in good condition. Take more than one, as you will need to break at least one open.
This site is not intended as a guide to identification. We can, however, point out some of the clues you should look for.