I haven't got a tutorial but i can tell you here. Very very easy.
Depending on the size of the head i normally use 12" for a newborn.....15" for 3-12 months and 17" for up to 3. Cut your elastic and sew together right sides facing. Then cut a piece of ribbon and hot glue it on the inside at the seam. Fold it over the front and glue on the inside again which forms a slight loop. That makes it interchangeable. I hope that helps. Sorry i don't have photos!