This question is motivated by this (highly recommended) comment by Emerton on Terry Tao's post "Learn and relearn your field". In particular, the following paragraphs:

In particular, the first couple of sections of Ribet’s famous Inventiones 100 article give a great example of how hundreds of pages of theory (including a lot of the theory of Néron models, and a quite a bit of SGA 7) can be summarized in ten or so pages of “working knowledge”.

and

For example, $p$-adic Hodge theory is another tool which plays a big role in a lot of arithmetic algebraic geometry, and which has a technically formidable underpinning. But, just like étale cohomology, it has a very nice formalism which one can learn to use comfortably without having to know all the foundations and proofs.

My question is: *Do you know of other sources that provide useful manual for your favorite technical topic?* (The kind of paper or section of a book which you use time and time again and would recommend for new researchers.)

As an example, where can I find the "nice formalism" of $p$-adic Hodge theory Emerton was referring to? (I was trying to learn more about almost ring theory from Gabber and Ramero - Almost ring theory and such a reference might be useful for bigger picture.)

Here is another example, just to fix ideas, since the question is a bit vague. At some point in graduate school I was trying to learn about "Riemann–Roch theorem for local rings". I found Fulton's intersection theory book, Chapter 18 and this paper by Kurano to be quite helpful.

This is obviously community wiki, so one topic per answer please. Answers with more description of the sources and how to use them would be very appreciated. Thanks a lot.