Aiden Pearce has a problem and you're going to try to help him solve it. You can do that by completing the various campaign missions. They make up a little less than one third of the game, percentage-wise. You'll likely want to spend plenty of time doing other stuff besides, but this walkthrough will focus on the missions you must clear in order to reach the game's closing credits. You can find other information and resources listed separately.
Keep I mind that there's often a variety of options when it comes to the matter of clearing a given mission, particularly some of the more advanced ones. Buildings often have multiple approaches, and you can often lean toward either hacking or blasting your way through Aiden's problems, depending on your preference. I've included just under 400 screenshots from my own trip through the game, to help establish reference points alluded to in the text. You can right-click to view the file path and open any of the images in a new window if you like, to view them at full size. Here in the guide, they're resized to prevent a bunch of scrolling. With that preamble out of the way, let's get to it!