There is no secret to 0V / GROUND.
Your power supplies (except in quite unusual situations beyond Arduino) should all have their 0V / GND wires tied together - no other topology makes sense.
This basic understanding of voltages (potential difference) is critical to wiring up any electrical circuit.
GROUND is a potential that is nominally equal to the surrounding electrical ‘environment’. POSITIVE voltages are those ‘above’ ground. +12V, +5V and +3V3 are the common positive voltages. NEGATIVE potentials are those voltages below ground potential.
In virtually every ‘standard’ Arduino project, there are no negative voltages exposed to the developer/user. Custom boards and interfaces may add ‘other’ voltages needed by the application.
So the take-away is : BEFORE you burn out boards, or start programming, make sure you have your hardware worked out. There’s no point putting fuel in your car if it doesn’t have tyres!
see also What is ground?