You can hook up an analog phone modem to your computer to send faxes (most analog modems can also fax). However, this means extra hardware, plus you need an analog phone line.

So usually an online service will be more practical. See this question:

electronic fax (sending) services

You can hook up an analog phone modem to your computer to send faxes (most analog modems can also fax). However, this means extra hardware, plus you need an analog phone line.

So usually an online service will be more practical. See this question:

electronic fax (sending) services