For anyone to use any cloud-based services or applications, they must have some kind of access to them. The portal is like a control module that provides that service. For there to be a portal at all, the virtual environment and base applications that run the whole cloud must be created as a base platform.
On the other hand, a cloud portal is a point of access for the cloud platform. Cloud portals are run using software that gives end users access to the virtual environment of the cloud platform.
They can be used to access applications developed on the platform like cloud-based SEO portal software.
A platform can host multiple portals. Portals can be private ones, built and accessed only by one company or organization, or public ones accessed by other users on a subscription, Software as a Service basis.
In the latter case, the portal is set up to host certain applications that end users can pay to access.