Firstly, connect the WS2812B to the Ameba board as shown in the following diagrams.

AMB21/AMB22 Wiring Diagram:

AMB23 Wiring Diagram:

BW16 Wiring Diagram:

To light up one individual LED or multiple LEDs with the same color, use WS2812B_Basics.
Open the example in “File” → “Example” → “AmebaWS2812B” → “WS2812B_Basics”

In the sample code, modify NUM_OF_LEDS to be the number of LEDs that you have connected.

Next, compile and upload to Ameba, then press the reset button. You will see the first 3 LED lights up with red, green, and blue light colors individually and after a while, all the LEDs will be filled with a color.

[1] WS2812B Datasheet:

https://cdn-shop.adafruit.com/datasheets/WS2812B.pdf