Where do I connect the ground pin of variable resistor, to the any metal part of project box or to the negative power connection?

 

It all depends on your circuit, but the GND connection you show would usually be connected to the 0V line of the circuit.

 

It all depends on your circuit, but the GND connection you show would usually be connected to the 0V line of the circuit.

Thanks

 

If you are using a 3-terminal potentiometer (volume control) as a variable resistor, there is no GND connection.
General practice is to wire the center tab to one of the end tabs for reasons of reliability.

 

What exactly is the pot being used for?

 

Another example of my pet peeve, the (mis)use use of GND has turned it in to a Homonym!
Max.

 

This is a typical noobie question I get asked:

"How do I connect power and GND to the pot to turn it into a variable resistor?"

 

Based on the notations that I see in the post, the intention is to use it as a potentiometer to provide a variable voltage. So the terminal marked "ground" should instead be marked as "common", meaning common to both the voltage source and the signal connection. On some occasions "common" and "ground" are connected, but mostly that is not the case. "Ground" is, in theory, an large plain of zero voltage and zero impedance. Mostly it exists in textbooks.