OK, remember how to put on a luggage tag? This is the same basic principle.
First, you need to measure and cut your fringe. Get a paperback novel. Wrap the yarn around it from the spine and across -- as if you were wrapping the book shut. Wrap until the book is covered. Then slide a pair of scissors under the yarn and above the spine. Cut. You'll have a bunch of pieces of yarn all the same size -- which should be twice the width of the book.
Each tassel will need three pieces of yarn so divide the yarn in piles of three. Each end of your scarf will need the same number of tassels so divide the piles in two (so if you have 14 piles of 3, each end of the scarf will have 7 tassels).
OK, ready to add your fringe? Get your crochet hook and look here.