Twist open a 4mm jump ring, string it through the crystal link hole, and twist securely closed. Repeat with the opposite side of the crystal link. For best way to open and close loops, see Jump Ring Hint in Jewelry Basics 101 (PDF).
Twist open a 5mm jump ring, string it through the first 4mm jump ring (attached to the crystal link), and twist securely closed. Repeat with the opposite side of the crystal link.
Connect a 5mm jump ring to the bracelet hook that is slightly longer. Use nylon-jaw, flat-nose pliers to compress the hook end and form a loop. This side is the fixed side of the bracelet.
Twist open the remaining 4mm jump ring, string on a crescent moon charm, and attach it to the fixed 5mm jump ring.