Stop Orders are normally used for one of two reasons, either to protect a position or to initiate a new one based on a projected breakout.

For someone who is in a position a protective stop is used to limit a loss or to protect profits. For example, if a trader is long corn futures from 380’ they may decide to put a protective stop in at 375’. This would mean if the market drops to 375’ they would sell their corn and liquidate their position.

Another use for stop orders is for an entry to the market, often at an area determined to be a breakout. For example, if a trader sees resistance in corn at 385’ they may place a buy stop at 386’. This would mean that if the market broker the area of resistance they identified at 385’ and traded to 386’ their order would put them long the market. If the market ever reached 386’ they would not get in.

Either way, stops have an important role in trading and are an invaluable tool to traders.

没搞过期货，主业术语不懂，勉强翻译以下，供参考。

止损令通常用于两种情况，即根据预见的突破点保护已有仓位或者建立新的仓位时。

对于某一持仓者，保护性的止损位是用来将损失控制在限度以内或保住利润。例如，如果操作者是在380’点位做多玉米期货的，他可能会将保护性的止损点设在375’，这意味着，当市场跌到375’时，它就会卖出平仓清算。

止损位的另一个是用场合是进入市场时，通常是在突破点位进入市场时。例如，如果操作者预见突破点在385’，他会设将买入止点设在386’，当市场突破385’指向 386’，他会买入做多，一旦达到 386’，就不再做多。