After posting a freelance job request, you can access it under My Requests from your Dashboard. You'll see recommended mentors below your request details. You can wait for mentors to reach out or browse through interested and recommended mentors.
If you've found a mentor that you think fits your need, you can message the mentor to discuss more details of your request.
If you would like to hire the mentor after the discussion, click on "Hire for freelance job" button from the chat window drop down menu (blue button). Enter the amount you have discussed and any descriptions and deliverables, and click "Hire & Pay by Escrow".
You can track the progress of your freelance job in the "Freelance Jobs" tab, which is accessible from your Dashboard.