Assume you're trying to buy at the bid and sell at the ask. The bid has a price and a volume on it, and so does the ask (volume of shares to buy/sell).
If you want to buy at the bid and then immediately sell at the ask, then you're doing short-term trading. The question is, is it possible to check short-term supply and demand by checking if the volume on the bid is higher than the volume on the ask? That means, is it possible to see if the price on the ask will stay the same or increase simply by just checking if the volume on the bid is higher than the volume on the ask?
Does that make sense?