http://www.3dgep.com/understanding-quaternions/ taught me a lot about quaternions. Quaternions are a 4D expansion of complex numbers, used to rotate points in 3D space by rotating them around an arbitrary axis. The blue line is the line being rotated, the cyan line is what the blue line rotates around, and the purple line is the final result.
From lots of research. By the way Wikipedia was too confusing for me.
