USB-C 3.1 (also referred to as Gen.2) brings many improvements to the previous standard USB3.0 (Gen.1). The most noticeable is the new Type-C connector which is much smaller than the previous standard connectors, it is also reversible.
Alternative Mode
The new Type-C Alternative Mode allows the USB cable to carry different types of signal, including but not limited to native DisplayPort capable of 4k resolution video.
USB Power Delivery v2.0
Wupports up to 20V / 3A (60W) of power. The new improved power delivery allows you to charge not only small mobiles devices such as mobile phones and tablets, but also laptops.
Reversible Connector
The new USB Type-C connector is smaller than most of the previous USB connectors. (Micro B is the exception.) It is also symmetrical; this allows you to plug the connector in either way up.