I'm currently working through Naive Lie Theory https://www.amazon.com/Naive-Theory-Undergraduate-Texts-Mathematics/dp/0387782141 https://www.amazon.com/Naive-Th

I'm currently working through Naive Lie Theory https://www.amazon.com/Naive-Theory-Undergraduate-Texts-Mathematics/dp/0387782141 https://www.amazon.com/Naive-Theory-Undergraduate-Texts-Math... by Stillwell and there's a lot about quaternions in the first chapter, including their standard matrix representation. You'd need to be familiar with some group theory to fully understand the 3D rotations but the matrix operations are clear enough to start coding with, I think.