How do I create a ground on a PCB when I also need a positive and negative voltage supply for an Op Amp? What even is ground?
In most electronic circuits, Ground is just the place in the circuit that the designer chooses to call &quot;Zero Volts&quot;, and use as a reference when measuring voltage elsewhere.  I think that this sort of Ground should really be called &quot;Common&quot; or &quot;Reference&quot;, but this misuse of the term &quot;Ground&quot; is so deeply embedded in electronics that we seem to be stuck with it.
In your circuit, the midpoint of the voltage divider across the battery is the circuit Ground.
In the other circuit, the midpoint of the voltage divider is shown as Ground, as are the mounting holes (H1, etc.)  All points with the Ground symbol (downward-pointing triangle) must be conected together.