A.1.1 How to show git’s output?

To show the output of recently run git commands, press $ (or, if that isn’t available, M-x magit-process-buffer). This will show a buffer containing a section per git invocation; as always press TAB to expand or collapse them.

By default, git’s output is only inserted into the process buffer if it is run for side-effects. When the output is consumed in some way, also inserting it into the process buffer would be too expensive. For debugging purposes, it’s possible to do so anyway by setting magit-git-debug to t.