Open a widget with its gear button, then click Widget Settings at the top. These settings decide who sees the widget. The widget's content is under Widget Content.
Display Groups chooses who sees the widget. Ctrl+click to choose several:
Click Save Changes.
Use it to show a "Sign up now" box only to logged-out visitors, or extra links only to admins. While you edit, master admins always see every widget, so they can change it.
For settings that apply to the whole container, see Container Settings.