Your "French Cuff" or "Rolled Cuff" shirts should have four small "buttonholes" in the cuff. You fold the cuff up in half, align all four holes up and slip one knot through all four holes. This leaves on knot on each outside of the cuff.
If your holes are not large enough for the knot to pass through you can try increasing the size of the holes with the zig-zig stitch on a sewing machine.
Or find a seamstress or tailor in your area.(a good place to look is your local mall where they have those places that will hem trousers. Anyone who knows how to sew a buttonhole can do this very simple job in about ten minutes.