What's the difference between Report Security Roles and Report Permission's?

The function of Report Security Roles is to enable administrators to restrict the visibility of certain data selections for specific users.

For example, you could limit a sales person to only see their customers, whilst allowing a manager to be able to view all customers.

In category permissions, you can see what access each user has for the category.

If the category doesn't show for that user it means they do not have any access to the category.