Macrame is the art of tying knots into patterns. Used to make jewelry, it's a simple craft that anyone can learn. It's very easy to make bracelets and anklets adjustable; you don't even need to know the size of your friend's finger to make her a ring.
Loop the cord and bring the end of the side underneath the loop over the other side; run it through the loop. This is called the overhand knot (when tightened); do not tighten it.
Bring the end of the cord you just pulled through the loop in the overhand knot back through the other way. Do not pull it all the way through, so it leaves another loop.
Hold both ends of the cord in one hand and the loop in the other hand; pull with both hands to tighten it. The end of the cord you brought through the overhand knot to make the loop slides easily, making the slip knot adjustable.
Slide the loop open large enough to admit the other end of the cord and use it to make another loose overhand knot, as in the Step 1.
Wrap the loose end of the overhand knot around the cord going toward the slip knot and slide it through the overhand knot. Tighten both knots, enough to hold the adjustable straps, but not so much that the knots do not allow the cords to slip through.