What is the difference between 'users' and 'customer portal users'?
Anyone whose email address is mapped to a user license from your account is a CRM user. A Zoho CRM user is someone who can manage records, either their own or those shared by other users, within the organization. In short, any employee who can access the CRM account to manage data is a user.
Portals are designed to give customers access to part of your CRM. Through a portal, your customers can access the modules and some of the associated data such as products, invoices, and notes. They can also view, edit, or create records or add notes and attachments. For example, if you run a school, instead of manually entering every student's details in CRM, you can provide parents with access to the portal. Parents can add, update, or view their child's details in the portal and the school can share the students' grades and performance scores with the parents through the portal. Read more about setting up portals here.