I need to provide access through joomla 3.6 backoffice to different groups of users: they must be able to SEE, create and edit only their categories and their articles. How can I do? With the ACL system I can only avoid that they can modify the items but can still see them. Thank you in advance
With ACL Manager (paid extension), you can use its enhanced ACL feature (from its options), to show only editable articles and modules to your users.
From the features description of the component:
Enhanced Joomla ACL
A selection of powerful additional ACL features on top of the Joomla ACL system like: Permissions per Module, Show Editable Modules only, Show Editable Articles only and Permissions for the Category Manager.