A) Customer self-service portal: A customer self-service portal enables customers to access self- service knowledge, support resources, view the progress of their cases, and provide feedback.
B) Community portal: A community portal leverages peer-to-peer interactions between customers and experts to organically grow the catalog of available knowledge from knowledge base articles, forums, and blogs as well as providing feedback through comments and ratings.
C) Partner portal: A partner portal allows every organization with resellers, distributors, suppliers, or partners to have real-time access to every stage of shared activities.
Ref: https://learn.microsoft.com/en-us/power-apps/maker/portals/portal-templates