The main command is:
git config --global core.editor "path to your editor with params"
Set up an editor and check it by making a commit:
git commit --allow-empty
Your favourite editor should open. Write commit message, save and close file. See git log to look for a commit. Is it there? If yes, you’re awesome.
git config --global core.editor "atom --new-window --foreground --wait"
git config --global core.editor "'c:/program files/sublime text 3/subl.exe' -w"
git config --global core.editor "'C:/Program Files/Notepad++/notepad++.exe' -multiInst -notabbar -nosession -noPlugin"