Yes, they are good for one year.
If you pre-purchase them through the member website or by calling Memeber Services, you will receive a voucher or will-call number. You take the voucher or will call number to guest services at any park or Downtown Dsney, where they will issue the pass. It is good for one year from the day they issue the pass. You can also just buy them when you get there, again at guest services. There is no pre-payment discount.