Just like @Ghanima said, the top two, labeled "RUN" are the reset pins, if you wire them together it will hard reset your Pi.
Now, as for the bottom two pins, the square one is ground and the circular one is TX. (signal)
If you have an old RCA cable you can strip the wire and solder the two wires directly onto the two pins like so:
and use RCA video out only. NOTE: There is no composite audio out on the Pi Zero without something fancy, like Hi-Fi Pi.
Image source: Element14