When you create a post or campaign, you select the brand that you want to appear on the post or campaign.
As an administrator you have access to all brands from the adhook account. As a user, you have access to the brands assigned to you.
You can manage your accessible brands at the top right of the gearwheel under "Brands". Depending on the menu item, it can also be called "Areas", "Offices" or similar.
Here you have the possibility to edit brands, add new brands or remove brands.