To send a fax login to your Press8 Control Panel at: https://manage.press8.com and go to: Actions=>Send a Fax.
Click on the "Browse" button to find the document on your computer that you want to fax. Then again click on "Browse" to find a cover letter (no necessary).
Under: "Send to" put the phone number you are sending it to without the dashes (eg. 5129988667), and it is not necessary to put a '1' if you are dialing US long distance, then click "Send".
You will receive an email telling you if the fax was successful or not.