What does this notation in the treble clef mean?
This is the symbol for a "turn" (the swirl, that is). Here's how I would play it:
The turn is positioned over the second half of the note; the "star" is not a star, but a double-sharp symbol, meaning that the "below" note of the turn (G) is a G-double-sharp.
(It usually helps if you name the piece: this is no. 4 in E minor from Chopin's preludes.)