A limit order is an order to buy below the current price, or sell above the current price. For example, if a market instrument is trading at 1.2952 / 55 and you believe that price is expensive, you could place a limit order to buy at 1.2945. If executed, this will give you a long position at 1.2945, which is 10 points better than if you had just bought the instrument with a market order. A stop order is an order where you buy above the current market price or sell below the current market price, and is used if you are away from your desk and want to catch a trend. If a market instrument is trading at 1.2952 / 55, you could place a stop buy order at 1.2970. In case the market moves up to that price, your order will execute and open a long position. If market continues in the same direction (trend), the position will bring you profit.