Thread:Project:Support desk/Sidebar editing doesn't work like described in 1.20.3

I'm going nuts now after trying to get any editing of the sidebar in a lot of skin types in any way described to work

when I access to /mywiki/index.php/MediaWiki:Sidebar all I get offered to edit is the mainpage, also some pages in the online help telling this way to edit the navigation bar are indicated to be outdated.

I'm using mediawiki the first time and like it because I use it as a reader on all sorts of pages and I can't believe that such a simple major thing is first: that bad described in the help pages, and: that bad documented in the code. (means hidden somewhere in skin and stuff)

may be I haven't learned much in 12 years php coding, satisfying hundreds of customers but for sure I'm too impatient to find out, what is easy for others.

Please help me quick 'how to edit sidebar' in standard not fancy skin.

cheers ralph