The purpose of a wireless router & a USB adapter
Wireless routers are devices that allow computers to communicate over a network, while USB (Universal Serial Bus) adaptors are usually devices that connect to a USB port on your computer.
Wireless Router Basics
Wireless routers connect a local area network of computers without needing to string Ethernet cables through walls or down hallways. This router can connect to a broadband modem and allow all computers on the network to use the Internet simultaneously.
USB Adapter Types
USB connections are popular for many external devices, such as printers, hard drives, flash drives and network connection adaptors.
USB and Wireless Routers
You can connect to some wireless routers with a USB cable instead of over-the-air. Other wireless routers come in a portable variety and establish network connectivity by plugging into a nearby computer's USB port.
The most common combination of a wireless router and USB adaptor is using a USB port to connect an external wireless network adaptor over-the-air to a wireless router.
If your computer has an internal wireless network card, you won't need a wireless networking USB adaptor to connect to a wireless router.