How do you know when to use a form of jambo vs habari?

Why is it only acceptable to use the you all form here? Hujambo was not accepted but it does not specify plural or singular you.

"Mnaendeleaje" too is a perfect translation

A jumbo ham?!?!?

Why cant I say Umedhindaje nyumbani?

How do you know when to use habari vs. a form of jambo?

Jambo means 'hi', not 'how are you?', right?

This bit is confusing coz the words look alike