Circuit Diagram
This provides a visual reference for wiring of the components. They aren't true to scale, just meant to be used as reference. This diagrams was created using Fritzing software.
Connections:
Gemma:
The GND is shared with all ground (-) connections.
D2 connects two of the LEDs, each on the opposite side of the crown.
D0 connects the other two LEDs.
220Ω resistors connect on the positive legs of the LEDs