The WS2812 is actually an RGB LED with a WS2811 built right into the LED! All the necessary pins are broken out to 0.1″ spaced headers for easy bread-boarding. Several of these breakouts can be chained together to form a display or an addressable string.
5V:This should be a regulated supply voltage between 5V and about 7V. More than that could harm the LED, less than 5V will either reduce brightness, or it just won’t turn on.
GND:The common, ground, 0V reference supply voltage.
DI:Data from a microcontroller (or another WS2812 pixel) comes into this pin.
DO:Data is shifted out of this pin, to be connected to the input of another pixel or left floating if it is the last link in the chain.