a usb is a "Uniform Serial Bus"
The universal serial bus (USB) is based on one port size and a matching connector. It is designed around the concept of a single host with multiple hubs able to provide uniform and simple addition and connection of various peripherals. The bus is designed to sense the addition or removal of a USB-compliant device and then automatically configure accordingly. The goal is to reduce the number of necessary cable connections and configuration steps. The USB is viewed as an inexpensive system for connecting low-data-rate devices. It is designed to accommodate transmission rates up to 12 Mb/sec. USB devices are designed so that several can be powered by a hub through the communication cable without additional power inputs
It is the little often oblong thing in the back of your pc..usually where your camera might go
and dongle is a device you need that allow certain softwares to run. It is a piece od hardware that plugs into your pc
hope this helps mate