As Windows user, one of the strangest things about Mac OS is a running, active application can be in focus without any actual windows open. If you use Command+Tab to switch between apps and don’t want to get stuck in no-open-window limbo, use the following key sequence to open a new window on your way there: Hold down Command+Tab, then press Option, then release Command. It doesn’t work for all applications, but it does for Safari and Terminal at least.