Suggest some Books and Tutorial for OGS Learning

Dear OGS Developers
I was going through the OGS benchmarks, but unable to learn OGS 6 from that. I don’t have a coding background and also, I have only basic knowledge about finite element method of solving differential equations.
Please suggest me some books and tutorials from where I could learn OGS 6 from very basic level. The already available benchmarks and docs are compatible for OGS 5, but I am not able to understand them while using OGS 6.
I am working on Groundwater Flow processes.
Especially I need help in editing prj and gml file. Also, please provide some information on various types of Boundary Conditions.