There are three ways of sending faxes from your personal computer:

1. Using an online fax service provider.
2. Using a (hardware) fax modem installed in your computer, along with faxing software (which may come with your operating system).
3. Using a fax server installed on your network.

1. Using an online fax service provider

Using this option, no installations of hardware or software are required. You simply sign up for a subscription with a provider, who will (1) allocate an inbound number for you, at which you can receive faxes, and (2) enable you to send faxes.

For fax reception, any fax received at the number allocated by the provider will be automatically forwarded to your email as an attachment. You will need a fax viewer to view these attachments, however, a fax viewer will likely be installed by default on your operating system.

For fax transmission, you will need to notify your internet fax provider of the address from which you send your emails. The provider will instruct you on how to format your emails, so that they will go out as faxes. Normally, this means modifying the "To:" address in some way. Once you send your email the fax gets sent out within a minute or two.

If you just need to send a quick one-time fax, consider using a service such as faxbeep.com which requires no registration and no commitment.

2. Using a fax modem and fax software

This option requires you to install a hardware fax modem into your computer. Almost all modems are nowadays dual-function devices, and operate as data modems and as fax modems in one device. The fax modem fits into an internal slot of your PC and connects to your telephone line via a regular telephone cable.

Additionally, you will require fax software, which lets you enter a destination fax number for your documents, manage your faxes, etc.

3. Using a network fax server

This option is similar to option #2 above in the sense that installation of hardware and software is required. However, the difference compared to that option is that only one hardware/software installation is required per network. This means that all users on a network can send faxes, without having anything installed on their personal computer. This arrangement is normally useful for office environments and not for home or SOHO requirements.

Usually, a small piece of client software is needed on each computer, which needs to fax. This is necessary to initiate the transmission of a fax and to manage the outbound fax queue. When a fax is to be sent, this fax client contacts the fax server and submits a document for faxing, along with information about its destination number and other parameters. The server performs the transmission itself, then reports back to the client regarding the outcome of the fax.

Check out the list of fax server products on Capterra, but note that some of these are actually online fax services.