How does one do WTB?

I need 2 Dali Mentor 2 woofers, but dont see an option for WTB listing
have often wondered the same ... USED to be easy but things have changed since I last posted one
Click on sell and fill out the information like you would if your going to sell then in the categories section select wanted
Is it suppose to cost the same as listing an ad?
After one posts a WTB advertisement, how does someone who has what you want send you pictures and how does the person wanting to buy the item complete the transaction within Audiogon?