Hello; how I can configure the messengin nethserver system and in what application y can work it.
What do you mean by messagging? Ejabber? Chat on webtop? Mattermost?
Ok so install from the software center, you can use AstraChat on android, but there are a lot of apps out there you can use. Log in using your admin account on nethserver. It pulls users/groups from the system users and groups so you can create a group called chat or whatever you wish and create users to go in that group and log in with any of those users.