When you find a project you'd like to do, you can bid on it.  At the bottom of the list, just enter you bid amount and an optional comment.  If you want to just leave a comment only (for example to ask a question), leave the bid amount blank...

 

   The bid requester will receive an email notifying them of your bid. When they respond to your bid, you will also receive an email with a link to their reply, so that you can correspond back and forth.

  To have the best chance of winning the work, don't forget to update your online resume in 'my registration'!