The lower piece fits up inside the upper piece and can be turned, and locked. On the lower piece are 3 small protrusions which fit into 3 vertical grooves on the inside of the top piece. Then you have to push the bottom piece up a bit and turn it as far as it goes then let it fall.
Inside you can have anything you want to carry with you, such as an ornamental stone.
The photos are of cage pendants made with the material "Black, strong and flexible". The quartz crystal inside (not included) measures about 3 cm along its length (about 1 and an eighth inches.)