Sew a seam down either side of your strap, so it’s ready to be sewn on to your bag. Loop it around your D ring, fold the raw edge underneath, and pin it to the bottom of your bag.
You’ll probably have to remove the extra part of your sewing machine in order to fit the bag around your sewing arm. I put my first strap on the back of the bag, on the opposite side of my design, so when I wear it the pretty lotus will face the world. Sew a seam at the bottom of your strap, securing it in place.