Do you need to volunteer before you can get anything from the Art Co-Op?

The Binghamton site says you need to volunteer before the Co-Op opens up for you, but our teacher says you only need to volunteer if you wish for an additional discount.

So do you need to volunteer before you could buy or just if you want a discount?

• And if you need to volunteer either way can you go in, sign up to volunteer and buy immediately or do you need to volunteer wait a few days until the volunteer time comes and volunteer before you can buy?