A rumor from one person and the same thing said by a hundred people carry different weight. It's the same with price: a rise on high volume means many people are buying. A rise on low volume can fizzle out at the first big seller. The same goes for a breakout of a level: on high volume it is trusted more. Don't confuse volume with the “Volume, $” field in the trade form: that's the size of your own trade.
Volume is usually drawn as bars under the chart: one bar per candle, and the taller it is, the more was traded.