Going Long – This means that you’re betting on the instrument (stock, future, option, etc) to go up and that you want to buy. You purchase the financial instrument, watch it rise and then sell it for a profit. Profit are realized when you buy low and sell high. It’s also known as taking a long position.
Going Short – This means that you’re betting on the instrument to go down and that you want to sell or take a “short position". A short position is closed out by buying those shares back or “covering" your position.
This concept is very confusing to new traders because you’re selling something that you don’t even own. The thing is that you’re still trying to buy low and sell high, you’re just selling high first and buying low later. Think of it this way – you go to a car dealer and order a new car, he charges you $20k and then looks to purchase it for a lower price. That dealer has taken a “short position" on the transaction between you and him. We don’t recommend new traders to take short positions until they learn more about the market.
One thing to keep in mind about short and long positions is that they’re totally different in nature. There are by far more traders out there taking long positions than those taking short ones. Human nature tells us that we buy with the expectation of rising prices. The concept of wanting prices to drop is against human nature and therefore short positions can be more erratic as a result.