The USB Soft Data Fax Modem is a type of modem that connects to your computer via USB and is used for dial-up internet connections, sending and receiving faxes, and other data communication functions over a telephone line. The "soft" in "Soft Data Fax Modem" usually indicates that the modem uses software-based signal processing rather than dedicated hardware, which can reduce cost and size.
The Windows driver for this modem is essential to allow your computer to communicate with the modem and use its features (internet, fax, etc.) on a Windows operating system.