There was a time in the history of macOS (formerly known as Mac OS X) when you had to use a Terminal command or a third-party utility to show the hidden files and folders littered all over your storage drive. I won’t go down the rabbit hole of why you would want to see these hidden files and folders, but know that Apple has finally built-in a simple keyboard shortcut to do just that—and it works in the Finder as well as Open/Save dialog boxes.
Simply hit Command + Shift + . (period key) and macOS will instantly make them visible (as seen on the right in the image above). Hit the shortcut again and they return to their hidden state.