Put 在 (zài) or 正在 (zhèngzài) in front of a verb to say that an action is going on, like "-ing" in English. Chinese verbs don't change their form, so this little word does the job. It is a core grammar point of HSK 1.
Subject + 在 + verb (+ object).
在 goes straight before the verb. In everyday speech, people often add 呢 at the end of the sentence as well. It makes the sentence sound softer and more natural, and does not change the meaning.
正在 works in the same place as 在, but puts more weight on "right now, at this very moment". In most sentences you can use either.
在 can also describe something you are doing over a longer stretch of time, such as these days or this year. 正在 is used less for that and more for the moment itself.
在 and 正在 don't mark the present tense. They show that an action was in progress at a certain time, and that time can be in the past. Give the time with a time word, or with ……的时候 (when...).
To say someone is not doing something, use 没有 before 在: 他没有在睡觉. In speech this is often shortened to 没在. A common mistake is to use 不 here: 我不在看电视 is wrong for "I'm not watching TV".
For a yes/no question, add 吗 at the end. To ask what someone is doing, use 什么 after the verb.
Only use 在 with actions that can be going on, such as eating, reading or working. Verbs for states, such as 是, 喜欢, 认识 and 知道, don't take 在. Say 我很喜欢他 (I really like him), not 我正在喜欢他.
Don't add 了 to a sentence with 在 or 正在. 了 shows that something has happened, while 在 shows that it is still going on.
Don't mix this up with 在 + place + verb, where 在 means "at". In 爸爸在家看书呢, 在家 tells you where Dad is reading, and 呢 shows that he is doing it now.
Practise this grammar point on paper: 18 exercises using only HSK 1 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 1. Paste your own sentences into the level checker to see which words, if any, are above your level.