When I was reading my book, I found the line below.

"Acting is all about revealing what it means to be human." Cate Blanchett says in it.

Although I know what "all about" means and "what" means "the thing that", I'm not quite sure where "it" relates to.

Honestly, I hava no idea about "it".

Please help me under stand "it".
Hi Liveinjapan

English syntax normally requires a subject for a clause. It is the subject of the clause but it doesn't really mean anything. Some grammarians call it a preparatory it.

It costs a lot of money to buy a car every other year.
It is advisable to leave now.
It was John that said something.
It is sunny weather.
It is two kilometres to the station.

Hi, Cool Breeze.

Thank you for helping me.

Now it's clear! Perfectly!

I'll call it a preparatory it too.

You helped me a lot!