mapping relation in table[linq]

Question

hello guys from last few days i was studying about linq .specially how to create strongly type datacontext and entity classes and how to map relation between to entity classes by using code editor(just to know what goes on background prosses) i understand most of those things but i am confuse about how relation  get establish between two entities . i found msdn have not much information about how things exactly work like this link i found http://msdn.microsoft.com/library/bb425822.aspx#linqtosql_topic3 its explain most of those things but not so deeply and here is another link i found http://www.codeproject.com/Articles/43025/A-LINQ-Tutorial-Mapping-Tables-to-Objects  which explain things better but i dont know from where these guys get this information even if msdn which is official site of microsoft doesnt have may i know any book which has every aspects of how linq work and how to make work it at its highest potential  

the things i am confuse about is how this key and that key properties work in assosiation attributes while mapping relationship

and please somebodu suggest me any book which can tell me complete picture of linq.

thank you