The two notes (A) in the bass clef seem to be played at the same time. However, this is music for piano, so I can't seem to figure this one out.
In this case, the half-note
A is struck ("articulated") at the same time as the eighth-note
A. However, while the eighth-note
A only lasts (brace yourself!) for one eighth note, the half-note
A must be sustained.
As such, you simply hold this
A down for the rest of the measure.
And, while I'm here, the notation in the left hand is a bit suspect, since the half-note
A crosses the mid-measure boundary; this is usually considered bad practice. I thought I'd supply a better alternative: