Go to Register, fill the form, check your email inbox and confirm your account by clicking the link
Go to My > My Lists > Create List, choose the collection (Album) insert your need and spare number of stickers card, each number delimited by comma or space.
Go to My Lists, press the swap icon . Choose the user you want to swap with and send a swap request to other user
When the swap request is accepted, put the stickers in an envelope and send it to the postal address that other user has gave you.
Once you receive the cards from other user don't forget to leave a feedback.