First, trace a circle on the back of your fabric. The bowl I used was 6 inches in diameter and it made a yo-yo flower that was just under 3 inches in diameter. (The rule is that it will be about half the size when you're done)
With the back up the fabric still facing UP, fold over a bit of the edge & stitch around. (Tip use a large piece of thread, because you need one single piece to stitch around your circle.)
When you've stitched around the entire edge of the circle, flip it over, and grab both of the knots you tied with your thread...
And gently pull them both at the same time...........
And keep pulling until it looks like this:
Then when it's pulled tight, tie your two pieces of thread together and cut off any excess.
I used a glue gun to add a large button to the center: