In "Apps management" you can set the configuration and customization of the desired app. The "Permissions" tab is the place where you configure the customization and configuration. Additional settings like "Settings" and "Maintenance" are described here.
By default apps are added with the Everyone has access checkbox checked. If you like to change the permissions on apps, you can uncheck this option.
You will see an overview with all the users and groups in the Workspace. You can assign permissions here.