A popover is a small panel that opens near the thing a person selected, showing extra information or a few related choices. It is like a note that appears beside an object when you ask for more detail.
For example, selecting a help icon might open a short explanation next to it. The panel can close when the person is done, keeping the main page visible behind it.
Keep the content brief and place it close to what it explains. If the panel contains a long task or needs the person's full attention, a larger dialog or page may be easier to use.