A very fast reader can read at a rate of one page every minute or two. No-one can read and make good notes at that rate. I have explained above how and why it is important to be selective about what to read. Equally it is important to be selective about what, of the material you read, you write down.
People vary immensely in the way that they read, the way that they take notes, and the amount of noting that they do while they read. The amount of note-taking that people do ranges from none (an almost universally disastrous strategy) to all; by 'all' I mean that their note-taking ends up by consisting of just copying out the important paragraphs word for word. I have, at times, lapsed into the 'all' technique and so I know from experience that it is an immensely time-consuming and completely unsuccessful strategy (because one is simply postponing the essential task of actively selecting the most essential material).
It will be for you to work out your own optimum strategy for note-taking. Most of the notes you take should be short paraphrases of what you are reading. Having decided that you need to note a section of a book, you should try to read one paragraph at a time and then note down a brief sentence or two summarising that paragraph. The notes need to be such that when you look at them months later (e.g., when revising for exams) they remind you what argument was being made, but they need not be in the form of full sentences, nor need they always be very detailed.
You should also always write down the author, title, date, place of publication, and publisher of the book or article you are noting, and make a note of which page of the publication you are noting as you go along – this information will be invaluable if you ever need to refer back to the material.
Generally, your account of the information and ideas you have learned through your reading should find its way into your essay in the form of an intelligent paraphrase, not a simple reproduction of someone else's words. A small amount of the material that you read, however, will be so crucial to the essay you are about to write, or so well-phrased, or perhaps so completely wrong (in your view) that it will make an ideal quotation to use in your essay. So, when taking notes, be on the look-out for a handful of good quotations, always making sure you do not fall into the 'all' mode of note-taking, which is, in fact, just copying out whole paragraphs and pages from the book.