If you have Windows 7, you can use the built in fax and scan program that comes with it. Since you neglected to mention what version of Windows you're running, that's about all I can tell you software-wise. You'll also need a fax modem which you can add inexpensively if you don't have one. They cost from $15 to $50 and come in both internal and external versions.
I am trying to set my computer so I can fax digitally stored documents on my computer to outside fax machines.
I currently have a Multi-Function Printer (HP Laserjet M1319F) attached to my Windows 7 computer (custom built) with a USB connection.
I also have a dedicated fax line and number which the MFP is attached to over a traditional phone/fax line. Traditional paper faxing works fine over the fax line.
Please let me know if I can with this hardware and if so, what I need to do from here. Thank you for your help.