A good grounding in the basics of the system will be achieved by studying these three free online sources:
The Riso Hudson materials on the Enneagram Institute website – How The System Works, Type Descriptions, and The Traditional Enneagram
Claudio Naranjo’s 27 Instinctual Subtypes
Caveat: Use “Sexual,” not “One on one.”
Eli Jaxon Bear’s Lectures on the Nine Types on Youtube
These are in order, beginning with 9, 3 and 6 – the central points of each triad – followed by the other types in the order they integrate: 5, 8, 2, 4, 1, 7. The whole playlist is posted. Click on the top left corner, where it says 1/9 – to see a list all of nine videos. Or click on the video, and the whole playlist will appear on youtube.