1. Explain it simply
在 before the verb means the action is currently in progress, like English '-ing'.
呢 at the end of the sentence is optional but common - it adds a relaxed, ongoing feel.
2. Show examples
我在吃饭。
Wǒ zài chīfàn.
I'm eating.
在 + verb
他在看书呢。
Tā zài kànshū ne.
He's reading.
在…呢 together
你在做什么呢？
Nǐ zài zuò shénme ne?
What are you doing?
Asking about an ongoing action
3. Share a tip
Don't confuse this 在 with the 'at (a place)' 在 - here it sits directly before the VERB, not before a location.