This summer some of my son's shorts were too big at the waist so my husband made a make-shift belt by tying a grosgrain ribbon around Nik's belt loops. It didn't look pretty but it did the job and helped keep up his pants! (I'm a big fan of recycling and I repurpose things when I can, for example, I usually save ribbon and string from packaging of products we buy...and that is where the grosgrain ribbon came from.)
After seeing the make-shift belt I decided to make a proper belt by sewing two D rings onto the ribbon. I took one end of the ribbon and folded it over the D rings and tucked the end under a 1/2" inch.
Stitch close to the fold of the ribbon and tie the thread ends. Cut off the extra thread after you have made your knots. If the end of the belt is unfinished, you might want to dab on a little fray check or fold the end over and sew it.