Andreas Meyer wrote:

Hello!

I am new to this list and wnat to set up a mediawiki for special purposes. At the beginning of the installation, if I remember right there was a question for the portal name

No. The question at install is the project name.

and now I want to change the name of the Portal-URL in the sidebar and don't know how to do it. Can someone help please? The sidebar looks like this at the moment:

* Hauptseite
* My-Portal
* Aktuelle Ereignisse
* Hilfe

and I want to change "My-Protal" to another name but with .../wiki/index.php?title=MediaWiki:Sidebar&action=edit this is not possible.

Yes, it is. See http://www.mediawiki.org/wiki/Manual:Interface/Sidebar You probably want Mediawiki:portal and Mediawiki:portal-url