Portals provide a UI for end users to interact with Dynamics 365 data. Previously Dynamics 365 portal was an add-on in an instance that was needed to be installed and configured under Applications

Now portals are available within Power Apps here

 

The Environments map to the instances and a portal can be created from the template available “Portal from blank” enter the name, address, and click on Create. Once provisioned it will be listed in the Apps grid

The portal can be edited from the context menu

What this will translate to in Dynamics 365 is an installation of series of Managed solutions in the Instance