What is the difference between a snail and a squid?

A snail and a squid? Really? Okay then. Well... (P.S. You misspelled 'difference')

Snail is a common name for almost all members of the molluscan class Gastropoda that have coiled shells in the adult stage. When the word is used in a general sense, it includes sea snails, land snails and freshwater snails. Otherwise snail-like creatures that lack a shell (or have only a very small one) are called slugs.

Squids are marine cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two longer tentacles. (The only known exception is the bigfin squid group, which have ten very long, thin arms of equal length.)