You can buy your tickets at any of the main gates into the park. The best bet is to get to the main gate in Wulingyuan as early as you can, the ticket office opens at 7.00 am. It’s always worth carrying your passport with you at all times in China – at most of the major tourist attractions you will need it, and here is no different. Your tickets (credit card style passes) are linked to your ID, and on your first time through the turnstiles they link your fingerprint to your pass!
If you’re a student, it’s worth taking the relevant ID with you as you’ll also be entitled to some pretty good discounts.