Some deal types require a parameter. If the type you selected needs one, the text field to the right of the deal type will become active, and you can enter the parameter there. You can also specify whether the deal type must apply to the dealer's hand or not. If you want to practice bidding 2NT openers, say, you can set Dealer Only, and open every hand 2NT, without danger of someone pre-empting in front of you. Bid now goes off and generates some deals for you, presents you with the first hand, and pops up a bid box.
Illegal calls are de-activated in the bid box.
The auction so far is shown under the hand, along with its high card point count, and losing trick count. As soon as you select a call, the deal disappears and the next one appears. The number of deals that it has generated. The number of deals that it has found which are of the type you specified. The number of deals you have completely bid.