Worsted weight yarn
Crochet hook size H
Pinning cardboard or pillow
Blunt needle to sew
With Worsted weight yarn in the color of your choice and H hook, make an crocheted I-Cord rope 19" long. Fasten off, leaving long tail to sew with.
If you don't know how to make the ropes, please refer to this tutorial: How to Make Crochet I-Cord Ropes
To make the frog, work as following:
Fold the cord in half, matching the ends. Cross the left end over the right one, forming a loop the size of the button you will be using. Pin in place. Curl right rope's end into a circle, insert end into the circle and pull a bit, as if you were going to make a knot, but not tightening into a knot, but leaving spaces in between, (it will look like a pretzel) bring the end up to one side of the button loop (turn the knot you just formed around, so that the pretzel part will be to the bottom and the end of the rope to the top, bring the top to the side of the loop that will form the buttonhole) and pin. Repeat on the opposite side. Now thread blunt needle with tail and sew, to secure the ends in place. Finally, take out the pins and stitch the middle, where the loop was crossed, to keep the button from slipping out. Fasten off. Sew frog to your bag, large purse or tote, leaving the buttonhole loop free. Sew button in place and you're done! You just got a handsome way to close your new bag.