They give you coordinates on a website along with a hint as to where to find the cache, You find them on a map or with your GPS,go to the location, try not to be seen by anyone who might steal or disrupt the cache( These people are refured to as Muggles), Inside the cache you'll find a pencil and Paper as well as a bunch of trinkets. You are to sign the paper as proof that youve been there and you may take a trinket as long as you leave one.The Caches are hidden and in watertight containers.
I went out today and I found 3 of them. It's actually fun. Like hide and seek for old people.