Question: How does the volume of a stock moving up and down affects the stock price?

It is exactly the same like let the water tap running into the bathtub. If you let the more water run (means more buying volumes) The water level in the bathtub is higher (price raising)

When selling is the same like let the water drain out from the bathtub. Water level is lower (selling mode)

Answer:

It doesn't, although if the volume is high, then the price move is considered more meaningful.

stock up, price low

volume itself is not a controlling factor in moving a share price either way.

it may accelerate a direction of price change but not initiate the change in the first place.

Some kind of news sparks the change....earnings report, a discovery of some kind or lack of expected results.

If the news is perceived as good then there will be more demand for the shares...causing the price to rise as everyone wants in on a good thing

If the news is bad then the volume increases as investors bailout on their positions.

But volume itself did not initiate the move....the good/bad news did....it just may accelerate a movement in one direction or the other