The second usage of le is to indicate the situation changed. It's normally after an adjective or at the end of a sentences. Since when the action is completed the situation normally is changed. It's also appeared as ...le...le. For example: 我买了书了。（wǒ mǎi le shū le) I have bought the book.

Here are some sentences: 1. Tiān lěng le。(It’s cold now.) 天 冷 了。 2. Xià yǔ le。(It’s raining now.) 下 雨 了。 3. Wǒ è le。( I’m hungry now.) 我 饿了。 4. Wǒ míngbai nǐ de yìsi le。(I understood what you mean.) 我 明 白 你 的意思 了。 Could you try to figure out this usage of le?