A: Profiles are your social accounts. For example: a Facebook Page, two Twitter accounts and a Google+ Page would count as 4 total profiles.
Brands are separate eClincher accounts that are managed by Agencies. For example: if an agency manages social media for 5 different businesses, they would set up 5 brands in order to keep each businesses data separate. Unless you are using an Agency plan, you will not have to worry about Brands.