“戒”是一个动作，“掉”是“戒”的结果。所以： （1）“戒掉”包括了结果，意思是要你成功戒烟。 （2）“戒”只是一个动作，成功还是不成功，你不确定。 汉语还有很多这样的词，一个动作+一个结果，我们把这个叫做“结果补语”。 例子：a,看，看见(结果) b.闻，闻到(结果) c,听，听见(结果)....... （我觉得你应该是中级水平了，所以我就用汉字告诉你。能看明白吗？）

"戒“and"戒掉" are both verbs. They mean "stop smoking". but "戒掉" is mostly used for a RESULT, which means have stopped smoking successfully via a period of attempt. “戒" also means a proceed to try to stop smoking. The two words are just as the similar with ”have gone to someplace“ and ” have been to someplace”. Hope you can understand it.

“戒”is a verb,"戒掉“means already “快点戒烟"focuses on the behavior,means start to give up smoking quickly: “快点戒掉烟”Focus on results,means succeed in giving up smoking as soon as possible.