This is the simplest way of attaching a second limb to a rope already tied to the body.

Be aware that while this technique is quick, easy, and popular, it is not particularly secure. Even with the line secured back to where it came from, any column tie of this general design (where you cross over, under, and tie a knot on top) can end up tightening -- under the wrong type of intermittent tension, the knot can pull away from the cuff even without slipping or collapsing, causing the cuff to grow tighter. For that reason, you always want to pay extra attention to monitoring this type of cuff.

In general, the Captured Overhand Cuff is a better technique to use in this type of situation. But here is the simplest way: