Why are there four inputs: DI and DO?
Those LED rings use the WS2812 LED chip on them, commonly known by their trade name NeoPixels.
They have 4 pins: VCC and GND for power, and Data In and Data Out for the control information you send them to control the brightness and colour.
Each ‘pixel’ takes a chunk of the datastream in through the Data In pin, then passes the rest on via its Data Out pin the whole way along the ring. The ring itself also has Data In and Data Out connections so you can string multiple rings together and feed them all from the same microcontroller pin.
The best resource I’ve seen for how to use these has to be Adafruits NeoPixel Uberguide, it’s well worth a read.