Go to an order you are interested in and click on Place a Bid button located on the assignment page. Enter the price you're willing to work for and any comments in corresponding fields.
Because there are no intermediaries, costs for assignments are minimal. To get your prices for an assignment directly from the writers you have to place an order to the Auction and wait for Bids from Writers.
In order to make a payment, you have to deposit funds into your virtual StudyBay Wallet (to your account). You can accomplish this using different payment methods, including bank cards, electronic money, PayPal, Webmoney, etc.