How do stocks like VUSA work?

I've read a lot and I don't understand how it tracks the s and p.

Are there individuals that are constantly buying and selling stocks in the top 500 listz and this tries to do what they do?

When people buy VUSA, does it, do anything to the 'stock' price? .. An example would be if I invested 20 million, would it make it, slightly jump, or so nothing because that's not how it, works?

Thanks