There is a road map for learning arithmetic algebraic geometry by Matthew Emerton here. Consider the following paragraph.
What is worthwhile, is to get a good understanding of sheaf cohomology in the classical setting. (The beginning of Borel's book on intersection homology which ultimately is about perverse sheaves and so on, but which begins with background on constructible sheaves and Grothendieck’s six operations, is one place to do this.) The point is that most applications of étale cohomology use just the same sheaf theoretic formalism as one has in the classical setting (i.e. varieties over the complexes, with their complex topology), and the main technical theorems in the subject (proper base-change, smooth acyclicity, nearby and vanishing cycles) are precisely intended to show that étale cohomology, étale constructible sheaves, and Grothendieck’s six operations in the étale setting, behave exactly as they do in the classical setting. So if one has a good understanding of sheaves in the classical setting, you can be confident that your intuition there will carry over to the étale setting.
Is it possible anybody could expand somewhat on the contents of this paragraph?