New Volto demo frontend

I want to contribute to the new volto frontend, the Contribution guide is quite confusing, can someone please help to set it up locally.

You need Volto and Plone installed, start here: Install Plone from its packages – Install — Plone Documentation v6.0

Awesome! Can you be a bit more specific about what is confusing to you? For core developers, it is sometimes hard to write good introductory material. It would help us a lot if you would provide some more details so that we can improve the onboarding process for new developers.

I am Trying to work on volto
there are two frontends for volto the classic one and the demo one,
I want to contribute to the demo one and not the classic one but the
shows us the classic UI development, how can I locally setup the demo UI for the plone6 ?