How to eat it?
The simplest method is to place the mangosteen in the palm of your hands, with the flower stem on top. Use your fingers to exert gentle pressure on it until it cracks open. Another option is to cut through the diameter of the shell all the way around, and then simply lift off the top. Just remember not to cut right through the segments.
How to store it?
Store on the counter, should be kept 15-25C if possible.