Folderstructure OH2

can somebody point me to the folder structure definition for OH2. Am a little bit lost compared to OH1.x seem for me a liitle complicated.

http://docs.openhab.org/tutorials/demo.html#installation

Is the folder structure different when installed though the apt-get package?

Yes, see http://docs.openhab.org/installation/linux.html#file-locations

Also see

http://docs.openhab.org/tutorials/migration

I seems though that totally different configuration files and directories are used. the /opt/openhab2/conf is not the place where files are like .sitemap, .persist, .items are located (manual installation from scratch, configured 20 homematic devices), or these files are not used at all, as I cannot find them anywhere.
Is there are place where this documented?

Yes.

Yes, that is the place if manually installed in /opt/openhab2.
items go to subfolder /items, persist files go to subfolder /persistence and so on.

Yes: see my link and picture above.

Most of the openHAB1 files can be copied to the new openHAB2 structure, for details see my link one post above.

Edit: or did you do an apt-get install? Then the files go to my picture described on the left side

I am not migrating from OH1.
I just have a friend who started some time ago and he was explaining the paradigm about OH. Now I do not see any of these files.
Where do I find all the devices which are accepted from the inbox. In OH1 these are in .items file.

Why are the binding in runtime:
/opt/openhab2/runtime/karaf/system/org/openhab/binding/org.openhab.binding.comfoair

openHAB2 has lot of differences compared to openHAB1, although it’s fully backward compatible.
I recommend to take a look at the docs, start with
http://docs.openhab.org/overview.html
and proceed to
http://docs.openhab.org/concepts/index.html
Bindings are not copied to the addons folder anymore, they are installed through a Graphical User Interface, preferrable PaperUI or Habmin: You will see an icon for PaperUI as soon as you start openHAB2.
In addition to that you may configure openHAB2 through karaf console if you prefer that.
Have fun.