About Tulle (pronounced 'tool'), just walk into your Joanns Fabric store (this is where I get all my tullle) or your hobby lobby and tell them you need pre cut tulle and they will direct you to where it is. Walmart does not always carry pre cut tulle.
First, measure the childs waist with measuring tape. Then you want to subtract 4 inches from that measurement. So if your childs waist is 20 inches then you want to cut a piece of Elastic that is 16 inches long. This allows some stretchiness to the tutu so it doesn't fall off your child ;)
Next you want to hot glue the elastic ends together one end overlapping the other. See picture.