Applying binding to straight edges is even easier then applying it to curved edges! You don’t need biased binding for straight edges.
Begin by pinning a length of binding to the straight edge leaving plenty of overlap on each edge. I am applying ¼ inch binding so I will sew just under ¼ inch. After the binding is sewn on, unpin, flip the binding up & iron flat.
Fold each tail end back over the binding & iron flat.
Trim off the lower corner to reduce the bulk. Fold the outside raw binding edge toward the other raw edges, fold over again making sure it covers the stitching line & pin. You can see step by step directions on fold back the binding here.
On the right side of the fabric begin sewing on the binding as close to the inner edge as possible without going off the edge & on to your main fabric.
Remove your pins, flip your project around & sew along the binding as close to the edge as possible without going off the edge. This double stitching, along the top & bottom of the binding, gives your binding a finished look.
Iron flat & Viola, admire your handiwork!
If you need any help, just ask!