USB hub is a small, light device that simplifies using USB ports in cases when there are too few of them (e.g. on some laptops) or they are situated at the rear side of your computer. Just connect it to the rear USB port of the PC with an extension cable and then place the hub where it is convenient for you to use it. It allows connecting up to 127 USB devices to a computer.
USB hubs are often built into computers, keyboards, monitors, or printers. When you see that such device has many USB ports they most probably stem from one or two internal USB hubs rather than each of those ports having independent circuitry.
The USB 1.0 specification was first introduced in 1996. It was developed to solve the numerousness of connectors at the PC's rear side and to simplify software configuration of communication devices.
The USB 2.0 specification was released in April 2000 and was standardized by the USB-IF at the end of 2001.
The USB 3.0 specification was released on November 12, 2008 by the USB 3.0 Promoter Group. It is up to 10 times faster than its predecessor.