Here's a breakdown:
* Chhota (छोटा) means "small" or "younger"
* Bhai (भाई) means "brother"
So, "Chhota Bhai" literally translates to "younger brother".
You can also use "Bhaiya" (भैया) which is a more affectionate term for an older brother, but it can also be used for a younger brother, especially if you're older than him.