I make mine out of buttercream right on the cake. I use a star tip (I prefer 32) and hold the bag perpendicular to the cake. Starting at where the toe is, squeeze a little (I usually squiggle it a little bit) and then move while squeezing to make the foot. When you get to the heel keep squeezing and pull your bag up to make the cuff. It should all be one continuous motion and you don't stop squeezing until the bootie is done. Then I take a tip #3 and pipe a little bow on it, on the top right where the cuff starts.