The above answer is very true, but personally, I wouldn't use them, they are designed to attract the little darlings, and they have an incredible sense of smell, so if you put them down, you'll get the Slugs and Snails from your neighbours gardens as well, and you'll have more than you started with.
The same is true of anything that attracts them, Beer Traps etc.
They die by eating them, the poison used is metaldehyde. Problem is, any bird eating the dead gastropod will suffer too. Also a no-no around fishponds.