There isn’t a lot of info out there about this feature and I am not exactly sure what it does (yet), but in case someone else wonders how to configure this…
How to start it
I couldn’t find it in the menus, so I just go Alt+F2 and then type “Cloud Storage Manager” and it comes up in the list.
Configure ownCloud
The first time you start this, there will be a big “Configure…” button screaming at you, or go Settings > Configure
This should open:
Click on “Add…” and select “Webdav”
It will ask you for your “Service Location”. Now this is where I got stuck. I’m probably just too stupid, but I was somehow expecting that to be the base URL, so like https://example.org/owncloud but instead it wants the WebDAV endpoint, which for ownCloud would be https://example.org/owncloud**/remote.php/webdav**
If all goes reasonably well, it will then ask for your username and password and hopefully log you in. You will know because it will report some storage figures.
Glitches
So far one problem that I have found is that it does not appear to let you configure more than one instance of a given type, so if you have an account on a second ownCloud or other WebDAV system, looks like you are screwed for now.
Also, it appears that you can name your account whatever you like, as long as it’s “webdav”. 
I am not entirely sure what the advantage of this thing over Dolphin may be yet. Maybe it synchronises content automatically? I haven’t found out yet. Anyway, there doesn’t seem to be much talk out there about this feature yet, so I thought I would contribute something. HTH.