In my opinion, the question is incorrect from the practical standpoint. Here is why: it implies that you think that "official documentation" is incomplete or unclear. My opinion is based on my other opinion: I don't think so.
Your question is also based on assumption that the documentation does not "satisfy" you. It means, that you don't blame your education, experience or capability, you blame some "defects" of the documentation. And I must admit, there are many cases when this is the case.
I, for example, can list a number of fields where Microsoft documentation is unclear, incomplete or even misleading. It happens, unfortunately. But usually, my knowledge of such documentation defects, real defects, is based on my research or practical experience, when I see that the behavior or data structure I can proof from, for example, debugging, in incorrectly described by documentation or not described at all. I shared some of such research results in CodeProject posts/articles, as other members did.
So, if you are really not satisfied, you should point out what exactly is unsatisfactory, with references. Everyone could use this information and thank you for that. If you are the person who can take responsibility for your own words. Otherwise you should simply say that you failed to understand certain moments, which would be fully respected by people.
Do you mean this http://msdn.microsoft.com/en-us/library/azz5wt61%28v=vs.110%29.aspx
If you can explain what part of it is unsatisfactory, you can get some chances to get more help.
Basically, you should think of device context as of some abstraction object which allows for uniform graphic processing for hardware or media with different characteristics or even different physical nature.