You'll need a pom pom maker for this, which is basically two pieces of cardboard cut in a C shape.
Place a strand of yarn through the middle of the pom pom maker.
Keep wrapping around and around.
Wrap until you've worked your way around the entire maker.
Take a pair of scissors and cut the yarn where it meets in between the two pom pom maker.
Cut a lengt of yarn and slip it between the pom pom maker and tie tightly around the pom pom.
Remove from the maker and you've got your first pom pom.
Make lots and lots of these in varying colours and types of yarn.
Thread a needle with a long piece of yarn, as long as you'd like your scarf but doubles over, so the needle is in the middle.
Tie a large secure knot at the other end.
Thread through the center of your first pom pom and then through a second.
Stop when you're scarf is the designer length and then knot the loose yarn.