That's not a chord.
You hold the G in the bass clef 4 beats, because it's a Whole Note (and the meter is 4/4).
The first G in the Treble Staff is played on Beat 2, and held for 2 beats because it is a half note. Then the G note is re-struck on beat 4.
The downstemmed G in the Treble Staff is there to show the descending melody line of G - F - Eb. Obviously you can't play two G notes on the same key at the same time.
So in essence, you play the low G on beat 1, the high G on beat 2, and continue to hold both, then on beat 3 you "add" the F note, then that moves to the Eb at which point the high G is struck again (so it sounds at the same time as the Eb).
The low G holds throughout.