Click here for the article on How to setup Dynamics 365 Portals in CRM Online?
Follow the below steps to have a look at the new portal editor preview feature.
Step 1: Login portal with Administrator user id and password.
Step 2: After successful portal login, admin can able to see Try new Editor button as a notification on the top of the page. Click on it.
Step 3: New editor page will be opened.
Explore the new feature and click here for more details.