The official site has more information. They suggest that you should register before May 29th; whoops, let's hope that their "before" is actually a "before and including" so that even this message doesn't come too late. :-) Once you've registered today, you can download the puzzles from tomorrow and the password to unlock them at 6pm BST (1pm EDT, 10am PDT) on Saturday 31st May. You'll then have 2½ hours to answer as many puzzles as you can. (Be sure to remember 2½. 2½ good. 3 bad. This was my biggest mistake last year.)
Practice is recommended, not least so you can find out whether you enjoy doing the puzzles or not in the first place. You can download past years' qualifying tests a link away from here, though sensibly (?) enough, for the early years, they will show you the answers on the page from which you actually get to the questions.
If you have Real Live Exams coming up, please steer well clear - but if you don't and you like the concept of spending a couple of hours doing puzzles against the clock then do look into it. Good puzzles, good fun!