Once a law firm posts an assignment, they will see the contract lawyers that match their criteria and invite the ones they are interested in hiring to bid on the assignment based on their profiles. You will receive and email and a notification on the K-Lawyers site if you have been invited to bid on an assignment. 

Enter your rate (hourly or flat fee, based on the law firm's assignment) in the Bid window and click Submit Bid.

You can always Edit or Withdraw your bid as long as the assignment is still open to accepting bids.