Aha. I missed that one.
Remaining the Admin Manual for Dummies 
But I realise that Nextcloud is kind of a swissknife and can be used in many different situations - from the user who wants to sync his computers, to the big company that use it for their intranet. So there is probably a need for a range of Admin Manuals for Dummies. I found the How-to/FAQ WIKI Thanks!