Completed Action with 了

了 (le) is one of the trickiest particles in Chinese, but at the HSK 1 level, its basic use is straightforward: place 了 directly after a verb to indicate that the action is completed. "I ate" is "我吃了" (wǒ chī le). "He went" is "他去了" (tā qù le). The 了 tells the listener that the action is done and finished.

It is important to understand that 了 is not the same as English past tense. 了 marks completion, and completion can happen in the past, present, or even future. "等我吃了饭，我们走" means "After I finish eating (future completion), we'll leave." However, at the beginner level, you will mostly encounter 了 used for actions completed in the past, and that is the safest way to start using it.

When a completed action has a specific object with a number or measure word, 了 typically goes right after the verb, before the object: "我买了三本书" (wǒ mǎi le sān běn shū, "I bought three books"). When negating a completed action, use 没 and drop the 了 entirely: "我没买书" (I didn't buy books), never "我没买了书." The 没 already implies the action was not completed, so 了 becomes redundant and grammatically incorrect.