This is the 10th most frequent Dutch word.
aan
"Aan" means "on," "at," or "to," depending on the context.
Here, 'aan' is part of the Dutch continuous tense construction 'aan het + infinitive', indicating an ongoing action.
Ik ben aan het lezen.
I am reading.
In this context, 'aan' expresses attachment or proximity, indicating where the painting is hung.
Het schilderij hangt aan de muur.
The painting hangs on the wall.
Here, 'aan' is used to indicate the recipient of an action, functioning as a preposition meaning 'to'.