Thank you again!

>> You mean in the preamble? I have mentioned it there:
>> \usepackage[style=authoryear,natbib=true]{biblatex}
>> \bibliography{<name>}
>
> The path is missing. The wiki clearly states that
> "Note that the bib file must either be located in your texmf-tree,  
> or you must
> enter an absolute path in the command above."

Yes, sorry, I have seen that, but as I looked for the database inside  
of Lyx I forgot, that I would have to enter it into the preamlbe also.  
The whole procedure is completely confusing for me, as I dont know the  
data management of my computer. Iīm normally just a user with no  
further interests in computers and programming, so this is really hard  
for me to understand.

And, honestly: I still donīt know what to enter. I tried two different  
versions, which both obviously donīt work:
\bibliography{/home/stefan/documents/Bibliographien/BibDesk/testbib}
and in german:
\bibliography{/home/stefan/Dokumente/Bibliographien/BibDesk/testbib}

here is he path as I would describe it
hd/user/stefan/Dokumente/Bibliographien/BibDesk/testbib

It also doesnīt work like this, but I donīt know how to enter it in a  
way, that Lyx could understand it.

> So write the full path to your working directory in the  
> \bibliography command,
> not just the file name. E.g.
> \bibliography{/home/juergen/test/bbl/testbib}

I also donīt understand this example: Do you have a folder with the  
name "home", or is this a certain folder which exists on every OSX?


> BTW if you use the biblatex module, you do not need a dedicated  
> bblscrreprt
> layout. The normal KOMA report layout will do as well.

Does that mean, that I do not have to install every class I want to  
use separately? That would be great! Just choosing the module in  
document -> settings -> modules?

Thanks a lot, best*
Jess