This can be achieved by providing information that is not factual or truthful. In essence this strategy relies on misinformation to raise the price of the commodity or the stock they hold. The price increase in such a case is known as pumping. The pump can reach several 100% within a few seconds to minutes.
Once the price reaches a desirable level, the account holder and all the pump and dump participants can start selling it off and that is what is referred to as dumping. That is what you need a little bit of experience to sell before the dump occurs.