Let us explain to you in very simple words as technology keeps defining new heights.
USB 2.0 operates at a max. of 480Mbps transfer data called “high speed” and it only has 4 pins. Generally defined in black color connector.
USB 3.0 operates at max. speed of 5Gbps transfer data rate called “super speed” and uses a blue connector to differentiate from USB 2.0 and has more pins.
USB 3.1 Gen 1 is the same as USB 3.0. USB 3.0 got a new name when the new speed USB 3.1 Gen 2 was released.
USB 3.1 Gen 2 data transfers up to 10Gbps, at 100W of charging power also known as “charger and cable clutter” is defined with a red connector.
USB is always backward compatible until the new USB-C where you may have to buy a new converter.
*source www.usb.org
updated 2018/04/01