I have been studying OpenFoam for some time, and it can be hard finding learning literature. Although for OpenFOAM version 2.1, the book was useful to me, I bought the book, and Dr. Maric E-mailed me today saying a OpenFOAM version 2012 book is freely available this next week. Today is 18th March 2021. His books cover OpenFOAM in detail! A good foundation after taking "Basic Series" or other tutorials.