This is "Augustus and the Sibyl" painted in the Italian north. The scene depicts a moment from medieval legend where Emperor Augustus encounters a pagan prophetess, or sibyl. She shows him a vision of the Virgin Mary and Christ Child floating above Rome, which is depicted here as a Renaissance cityscape.
The figure on the right, the sibyl, looks quite astonished, throwing up her hands in response to what she sees. According to the legend, Augustus was shown this vision on the day Christ was born, and it's said that he set up an altar dedicated to the firstborn of God as a result.
The painting is done in oil on poplar wood, which gives us some clues about its history and how it might have been displayed. It's possible that this small panel was once part of a larger piece of furniture or decoration.
Augustus and the Sibyl hangs in The National Gallery on Trafalgar Square, London — free to enter. Point your phone at any artwork there and audioguide.london plays a free audio guide in six languages — no app download needed.