Snails do not have legs, but instead have one very large and very flat foot. Snails secrete a layer of mucus that they use to help them glide about.
The snails' foot is not really a foot in the conventional sense, but instead is a muscular organ that is spread out beneath the body of the snail. The snail makes a rippling motion with the muscle, and as it moves, it secretes a bit of mucus that coats the ground beneath it and helps move it along. The snail leaves a small trail of slimy mucus behind wherever it goes, although this is only true of most snails, not all.