you can use one rectangle of fabric if you want, but if you don't want the fabric to fray, you should cut two.

you'll also need a small piece of ribbon or a thin strip of fabric. about 3 inches long.

lay one rectangle of fabric on the other, with their outsides facing each other.

sew around the edge, but leave a gap between where you start and finish, so you can turn the fabric right side out.

turn it right side out and sew around the edges (or you can just slip stitch the small gap closed).

lay the ribbon across the middle of the rectangle. pull the ends of the ribbon together behind the rectangle, and pull the ends tight until it scrunches into a bow.

it should look something like this. you can tie the ribbon in the back, or secure it with a few stitches. you can attach it to a hairclip or a skirt/dress/whatever.