All you need is your internet connection and you're good to go...
You'll want to use an online/internet fax service, there are plenty to choose from and depending on your needs, these are probably the best to choose from:
https://www.wiredfax.com/ - $5.95/month
This is what I use, if you're like me then you have a scanner or digital camera and you know how to email people for free. However, you still need to be able to receive documents from people who only use fax. That's why this is perfect, it's an incoming/receive only fax service and it's unlimited. You receive faxes via your email and then you can simply print out documents if needed.
http://www.faxzero.com/ - FREE
Or at least this is as close to "FREE" as it gets for fax services. You have to send faxes with advertisements on them and there are many limitations.
http://www.efax.com/ - $20/month Average
This is what you'll want if you absolutely need a full featured fax service and do a lot of faxing. Be warned though that they charge you extra per fax if you go over a certain limit.
Good Luck!
Thanks, GladToHelp