Every so often, a new light is half-lit, prompting a search for a new 3-number combination sequence. There are 10 lights, 10 slots. A successful unlock gives a 'reward', anywhere from a video, to documents, to websites.
Scattered among various pages and websites are symbols (runes) that only after some received a coded document began to make sense. That letter became the initial 'key' for decoding further appearances of the rune.