To crawl
If you let a snail crawl on a glass plate, you can clearly see how the animal moves. A snail moves by making undulating movements with the bottom of its body.

Snail-like animals that do not have a shell are usually called slugs.

Slime
The foot is lubricated at the same time with mucus from glands on the bottom of the snail. The stuff is left on their way like a slippery trail. So snails produce slime to make crawling on the ground easier.

Land Snails aren’t able to hear at all, but they have eyes and olfactory organs. They use their sense of smell to help them find food being their most important sensory organ.