Send your client's trip from the request form at the top of the Trip Desk. Every Confirmed operator whose fleet fits the trip hears about it, and the bids come back to you at wholesale. Bidding stays open until you book, and we email you new bids every 15 minutes.
To ask particular aircraft, use Search aircraft. It shows open aircraft near the departure with estimates from each operator's rates, and you can ask those operators for a firm quote.
Travelers who send you a request arrive on the same Trip Desk, with the operators' bids already coming in.