How can I make an app close when it refuses?

To avoid clogging memory, quit an app when you stop using it (File > Quit or Cmd-Q). If the app’s “hung” and ignores you, hold Opt, click and hold the app’s icon in the Dock, and pick Force Quit. Or choose Force Quit from the Apple menu (Opt-Cmd-Esc) and pick an app. Unsaved work may be lost.