Historians refer to anything recorded by people who participated in or observed an event as a primary source. Anything written later is a secondary source. A textbook is, obviously, a secondary source, and so are lectures. Most of the things you will learn in class will come from secondary sources, but in order to really understand how we create knowledge about history you need to work with primary sources. Primary sources are usually trickier to work with than the secondary sources that are likely to be assigned in your classes. Textbooks are written to be understood by 21st century American students. Even monographs and journal articles are aimed at modern scholars. Primary sources are written (of course they can also be things like posters or photographs) for very different purposes and aimed at very different audiences, and you have to ask yourself  new questions about the reading.

Who wrote this, why, and for what audience?
People don't write things for no reason. This was written to tell something to someone, and odds are it was not to tell history  students something about this society. First, you need to ask yourself how much this person knew about what they are writing about. Then consider who they were writing to, and what they were trying to convince them of or tell them. All of these things are vital to figuring out what can be learned from a text.

-Who wrote this? If this source is from a published source reader there may be a brief introduction explaining who they are, or you may have to do some digging. Often it is enough just to know what type of person they were (a London journalist of the 1920's, a Salem whaling captain of the 1790's). Who they were will ofen tell you what they might know about a topic and what point of view they may be bringing to it. The medeival inquisitor  Bernardo Gui was quite knowledgeable about heretics (he spent his whole life hunting them) and thus is a valuable source, but his take on the Albegensians is probably very different from what one of them would have said.

-Why was this document written? Who is the audience? Different types of documents were created for different purposes and will create different problems of understanding and interpretation. A memo from the Navy Department to President Roosevelt on the progress of the war in June of 1943 will probably not explain how we got into the war and will assume that you know who 'Stimson' is. It is probably also trying to convince the President of something or maybe even hide something from him. You need to be able to situate these documents to be able to get meaning out of them.

What can we learn from this document?
This can be done at several levels. In some cases a document will tell you quite directly what it is doing. The Communist Manifesto is a good example. As the title implies, it it is a manifesto intended to tell people the beliefs of a group of people. It is written in clear, direct language that is easy to understand with minimal background. Some documents may be far more technical or focused on a particular audience and this may matter a lot. A speech by Lenin to his followers might discuss only very briefly some points that you think are quite important, on the assumption that the audience will understand them already. Even a simple document like the Manifsto can be a little deceiving. Marx is claiming that he is presenting a definition of Communism that is accepted by all Communists, for whom he is the accepted spokesman, neither of which is entirely true, of course. You need to be wary of assuming that your writer is telling the truth to you or to themselves.
    Besides the things that can be learned from the direct statements that documents make, you can learn a lot about the implicit assumptions of an individual from the things that a document assumes or does not bother to say. Marx is not much given to quoting the Bible, but he is fond in many of his writings of citing statistics, revealing something about what he considers to be the source of intellectual authority. You can also learn a lot about the people Marx opposes, although describing them is not really the point of the piece.
    Finally, you can sometimes learn about the social world that people lived in. A person from Mongolia whose only exposure to American society was watching Desparate Housewives would have a very warped view of what Americans act like (and look like) but would probably know quite a bit about what we consider normal behavior and how we deal with each other.

Producing something
What the final product of your reading is depends on why you did it in the first place. If you were reading it for a research paper you should be looking specific facts that will help you make your points. I may also ask you to write a source analysis paper. This is usually a short (2-4 page) paper that explains
-What the document is
-Who wrote it and for what audience
-What things we can learn from it (This is the most important).

Writing an analysis
    Once you have figured out what you would like to say then you can figure out how to organize your essay. Do not summarize the reading. You should answer all the questions I gave to you, but some of them may be less important than others for this particular reading, and thus should take up less space. The paper should be organized around your ideas, rather than the format of the reading. Although  your author may treat things in a particular order or spend more time on some things than on others, that does not mean that you should follow the same format. This is often the hardest thing for students to get the hang of. The organization of the reading is more or less handed to you, and it is the easiest way to organize, but what you need to do is to force the material into your own structure. This is your essay, organized around what you most want to say about this reading. You don't necessarily have to deal with all the questions I mentioned above at the same length. It is perfectly o.k. to focus on the things that you think are more interesting or more important, but you need to make it clear why you are focusing on this and why the essay is written the way it is.

Here are some more tips on writing.