It depends on which market you are trading. Let's simplify the explanation of some folks above.

- "Buy" and "Sell" are only available in the spot market.
To make a profit, the only condition is that you buy low and then sell high.

-"Long" and "Short" are only available in the futures market.
This goes both ways to take profit. You open a "long" position, then you should close the position at a higher price. Conversely, you open a "Short" position, then you should close the position at a lower price.