The context is from Forbes on youtube.
Around at 06:24 How To Ace Your Job Interview Over Zoom | Forbes
You need to know what you want them to understand about you.
what does this sentence really mean?
Is it like
You need to know something about you and you want them to understand that thing.
Also I am not sure about the usage of
Suppose a document is about you.
Ask: What is it about?
Meaning: What is this document about?
Meaning: The document could be about a house, a room or a dog...
Another ask: What is it about you?
Meaning: It could be a recording or a video about you.
Is my understanding correct?
Please shed light on my doubt.