For those who just begin to study Mandarin Chinese in China, they should know the character 了in Chinese language is a modal particle. When it is used at the end of a sentence, the modal particle 了implies a change of state. For some examples, 他已经参加工作了, implying he didn’t have a job in the past. If you say她又想跟我们一起去了, you may mean to express she didn’t want to go with you originally.

There are also some other typical examples such as 树叶已经黄了and这件衣服小了. In addition, you should know the structure 不…了also implies a change of state. For some examples, 结婚后，她不工作了, implying that she still worked before the marriage. The sentence 我今天不发烧了carries the meaning that the speaker still in fever yesterday.

What’s more, it is important for those foreign students who learn Chinese online free to learn the structures such as 要…了，就要…了，快要…了，快…了, which are applied to indicate that something is about to happen. If teachers say 要上课了, it means the class will begin soon. If you say 再有两个月就要放寒假了，you mean that the winter holiday will come after two months.

But one point needs much attention when you learn Mandarin Chinese is that if there is an adverbial in a sentence to specify the time, the structure 快要…了is not allowed. For instance, since the sentence 下个月姐姐快要结婚了has specific time 下个月, 快要结婚了is not proper. Instead, we should say it as 下个月姐姐就要结婚了.

Besides, some sentences in Chinese language have no subjects, including some sentences with the character 了. The function of theses sentences is to describe some natural phenomena such as weather. You can say刮风了，打雷了and 下雨了.