Главное меню

Try:
Admin panel > View Plugins
Try to drag& drop any plugins....you will understand

With drag&Drop you can manage order of plugins in menu....try

I know it. Multimedia menu items will be at the end of the list of 15 items. And I need a separate list of the 3-point multimedia menu and a separate list of 12 items remaining.
I need two drop-down menu list.

I know, I understand what you mean, but don't forget that default menu for SE is made for total dummies - people who know about codings, even basic, nothing. So, I stand beside my statment - why waste time to make this mod, because this is pretty big job for nothing. The most easyiest way is construct custom menu - and this is it!
Personaly, I won't waste my time to crack my head making this non-needed mod. Also, I dont have enough knowledge to do this as quality job.
Maybe you know way how to make this type of meny, I don't..

p.s. It's simpliest way is to use comment {* *} to disable non-willing menu, in case of disabling it(them) ....