Hermit crabs find and choose their shells by using their sense of touch and smell. They are constantly on the lookout for new shells to move into as they grow, and they use their antennae to feel the inside of shells to see if they are a good fit. Hermit crabs also use their sense of smell to detect if a shell is suitable for them based on factors like size, shape, and cleanliness. When they find a shell that meets their requirements, they will move into it and make it their new home.