Andrea painted this early work for the convent of San Gallo; it is presently in the Palazzo Pitti in Florence. The tiny extra scene behind Mary and the angels is usually interpreted as Susanna and the Elders - a Susanna who resembles a male nude but who in her concern for her chastity is a type for Mary;
the two Elders are pointing to her from on high.
The figures of the Madonna and the Angel Gabriel in the foreground, accompanied by two other angels, are full of gentle human beauty, vibrant with poetic intensity. Also in the scene above Gabriel's head appears a cloudlike formation which may represent God the Father whose word it is that the angel pronounces to Mary.
There is also a descending dove, symbolic of the Holy Spirit descending upon Mary along with the Father's word, as it did upon Jesus at his baptism (Matt. 3. 16).
In the angel's hand is a flowering staff, representing the staff of Joseph which blossomed as a sign that he was chosen to be the earthly husband of Mary. See the Monastery Icons website: "Searching for a righteous man with whom they could entrust the youthful Virgin Mary in marriage, the priests of the Temple called all men of the tribe of Judah to bring their staves into the Holy of Holies. The staff of the righteous old man Saint Joseph miraculously blossomed. And so he was chosen to be the spouse of the Blessed Virgin." Mary's symbolic flower the lily is on the angel's staff and around her are scattered white and red roses signs of her purity, passion, and love.
You can see a large image at Web Gallery of Art: