To turn on the Preview option please follow this blog post:

Your video page will start to load for the first time so this may take a while (about 10minutes)

Once Completed you will receive this nice Welcome Message , click Let’s go

One of the first things to note is the URL of the Video Portal

https://yourtenant.sharepoint.com/portals/hub/xxxx

So let’s create our first Channel

Click the Create Channel Button , Give your channel a name and color:

Click Create

Once created you can now upload videos and share with your Security Groups, SharePoint Groups or even unauthenticated users(everyone).

If you have some movies you can also use Sharegate to migrate you movie files to the Microsoft Video portal.

For more information you can check this blog From Jasper Oosterveld about Next gen Portals.

You can also check this Blog of Benjamin Niaulin.