Through the Users - Management section you are able to limit the information each user can access through the app. This may come in handy if you have people selling different products and the other groups or categories are irrelevant to them.
To limit user view ability simply go to the Management tab under Users in the left sidebar and select the user you would like to edit. In the "Edit" section you have four options as to where you set the limits: Roles, Content Languages, Permissions, and Groups & Categories.
Roles and Permissions
When you select a Role for a user, default Permissions will be applied to the user. If you wish to assign the user more permissions or un-assign them any of the default permissions, you can go through the permissions list and manually choose which ones you would like that user to have:
Groups & Categories
Users can be granted the ability to view or edit certain groups or categories based on the role and permissions selections for that user. You can choose whether each user has the ability to view or edit the content of specific groups and categories. This is based strictly on role, so not all roles will have the edit option (viewers do not have edit capabilities at all and can only view, for example):
Once you are finished click "add" and then "Save" and that user will have limited access to information.