how to insert a new forum not in the end of forums list?

I hope I have not misunderstood your question .. You Add forum and then Edit that forum - You can change forum name, description, and order there .. and much more, if you study the manual =:)

First, you need to Add this forum under administrative panel. Then below the adding/editing forum, you will see the list of forums. On the right hand of each forum, there are ↑ and ↓ symbols. Clicking them, you can move the forum up and down, aligning it in the place you want.

Thanks! It's clear.

I studied but not complete.

I've thought it's obvious on the editing page :)
But the Manual may miss some points. It's too outdated - must rework it after I've done with the root miniBB.

English is not my native language and I read English texts at the worst :)

It's so obvious... up and down arrows - they do not have a translation.
Anyway, good it works for you now :)

Yes, after explaining it's much more easy to use.