Your downloaded Zero One theme files contain everything, so you don't need to download anything from other sources.
We suggest you leave a copy of the original files as a backup if you accidentally delete something.
Extract all files from the .zip file (be patient, it takes some time).
What is in download files:
Zero One theme main demo --
Zero One premade demos -- example
zero-one-consulting folder, etc.
Documentation link file.
But first, please read all sections from installation docs.
Learn in detail on Kirby website -- https://getkirby.com/docs/guide/quickstart#requirements
PHP 7.2, 7.3 or 7.4 (PHP 7.3 is recommended)
All of that is almost default setup at majority hosting providers.