From the introduction:
Welcome to one of the most ancient, and certainly the most advanced, race present in the Koprulu Sector. The Protoss. This race is one of the oldest space faring species to travel the stars since the Xel’naga. As such, they often refer to themselves as the Firstborn. Despite being an advanced race, they are somewhat tribal in nature, and have split into multiple different factions over the years, with radically different living styles. A species without a mouth or digestive tract, they instead use photosynthesis, gaining their energy from sun or moonlight. What little moisture and nutrients they require are absorbed through the skin.