yeah~the particle“了”is really important in chinese~ if you make full use of 了，your chinese will be more vivid~ #1 了“le”---the most common ：follow the verb when you want to express that the action has done： eg： Mom:吃饭了嘛? You:我吃了。or 我吃了饭。or 我吃饭了。 or 我拍吃了饭了 。 many oral sentences：下雨了，不去了。气死我了。吃饭了。吃了饭。停电了。 #2 了“liao”---more documented：to finish eg：了结；了断；一了百了。（the 3 words is common，enough for u :) ） 我要和女朋友分手，一了百了！ #3：了解“liao jie”：know&understand eg： 我了解 i understand（such as the event or case） 。 我了解他 i know him 。 我很了解他 i do know him ！ ..............................hope that helps

“了”often be used at the end of a sentence. It sometimes works as particlea,to indicate that sth new had happened. when it goes after a verb or an adjctive,it means the action or the change had been complicated."I drank 3 bottles of water" means 我喝了三杯水 in Chinese，it means the action of drinking has been done.so it is the later sentence我看了一部电影。Both two sentences indicate that you have had finished your action.

动词+了 我喝了三瓶水。 我看了一部电影。

This is very easy. Use it as when you use the English word "already".

例子：用“了” 说 “I drank 3 bottles of water.” 和 “I watched a movie.” 一样吗？ 嗯。但了的用法远不止表过去式，完成式。更不要提俗语，口语中的一些特别的用法。我至今尚未见到过什么特别详尽的语法解释。