I know how to add element to onepage, but I want to create separate page/no onepage and add this page to menu. Its possible to do that in this or similar skeleton?
Are you just asking to put a link in the menu of your site that redirects to a URL outside of your site?
If so, make a page and name it what you need to, then go to the Advanced tab. Here you will find a field named Page Redirect. Fill in the URL you need and save it and that should work.