This is in the Mac Help files:
Sending a fax
You can fax files directly from your computer to any fax machine or computer that is set up to receive faxes. If your computer has a modem that is connected to a phone line, it is automatically configured to send faxes.
Choose File > Print, and then choose Fax PDF from the PDF pop-up menu.
Type the fax number in the To field, or click the Address Book button to the right of the To field to select a number.
If your phone system requires you to dial a prefix for an outside line, type it in the the Dialing Prefix field.
Make sure the correct modem is selected from the Modem pop-up menu.
To change your options, choose the option category from the Fax Cover Page pop-up menu. For example, to fax more than one copy of the document, choose Copies & Pages, and change the value in the Copies field.
Click Fax.
The fax is sent as soon as your modem is available. For example, if you're using your modem to connect to the Internet, the fax is sent after you disconnect from your Internet service provider.
If you want to paste a number into the To field and the Edit > Paste command is not available, Control-click the and choose Paste from the menu that appears.
To send a cover page with your fax, click the Use Cover Page checkbox, and then type a subject and message in the text boxes.
To choose your modem's behavior when faxing, choose Modem from the Fax Cover Page pop-up menu. You can choose whether to dial with touch tones or pulse tones, whether to listen to the modem as it dials, and whether to wait for a steady dial tone before dialing.
To send your fax at a later time, choose Scheduler from the Fax Cover Page pop-up menu and enter the time. Make sure your computer is on, is not in sleep mode, and is connected to your phone line at that time.
If you have a set of options that you frequently use, save it as a "preset." After you set your options, choose Save As from the Presets pop-up menu. To use this set of options when faxing another document, choose its name from the Presets pop-up menu
See also
Faxing
Print options
Open this for me
Address Book
If you click on the 'Faxing' link at the bottom then click on 'Setting up you Mac to receive Faxes' you should be right to go.
If you have any problems feel free to post back.