在 / 正在
zài / zhèng zài
Expressing actions in progress with "zai"
在 in front of a verb marks an action happening right now.
(正) 在 + Verb
How it works
我在吃饭 means "I'm eating" — in progress at this moment. 正在 is a slightly more emphatic version, and 呢 is often added at the end: 我正在吃饭呢.
This 在 is a different animal from the 在 that marks location, even though they look identical. Before a verb it means "in the middle of"; before a place noun it means "at".
Negate with 没: 我没在看电视.
Examples
wǒ men zhèng zài chī fàn
我们正在吃饭。
We're eating right now.
tā zài dǎ diàn huà
他在打电话。
He's on the phone.
nǐ zài zuò shén me?
你在做什么？
What are you doing?