Q2. What are different portals in Salesforce.com?
A partner portal allows partner users to log in to Salesforce.com through a separate website than non-partner users. Partner users can only view & edit data that has been made available to them. An organization can have multiple partner portals.
For partner portal best practices please refer link:
Customer Portal provides an online support channel for customers allowing them to resolve their inquiries without contacting a customer service representative. An organization can have multiple customer portals.