已经 (yǐjīng) means "already". It almost always comes with 了 at the end of the sentence: 已经 + verb + 了. Together they say that something has happened, or that a situation has been reached, by now. It is a key grammar point of HSK 2.
Subject + 已经 + verb + 了.
已经 is an adverb, so it goes after the subject and straight before the verb. The 了 at the end shows that the action has happened. You could also just say 我吃饭了, but 已经 adds the idea that it is done by now, often sooner than the other person thinks.
已经……了 also works with adjectives, clock times, ages and lengths of time. It says a point has been reached. With a time or a number and no subject, the sentence can begin with 已经.
With a length of time, as in 两年, you can use 了 after the verb as well as at the end: the action began in the past and is still going on.
In English, "already" can go at the end of the sentence. In Chinese, 已经 never does: say 我们已经到了, not 我们到了已经. It also does not go in front of the subject, so 已经他回家了 is wrong.
The other common mistake is to forget 了. 我已经吃饭 sounds unfinished to a Chinese speaker. Keep 了 at the end of the sentence.
The opposite of 已经……了 is 还没有 + verb, "not yet". Do not use 已经 for this, and drop 了: 我还没有吃饭, not 我已经没有吃饭了. With 不, 已经不……了 means "no longer" or "not any more".
To ask whether something has already happened, add 吗 to the end. Answer yes with 已经 + verb + 了, or no with 还没有.
Practise this grammar point on paper: 20 exercises using only HSK 2 words, with an answer key on a separate page. Free to print and copy for your class.
Every example on this page uses only words up to HSK 2. Paste your own sentences into the level checker to see which words, if any, are above your level.