christian70, thank you very much, qtranslate meta field is under the main content indeed, I didn't saw it there! :))
All-in-one-seo and seo-by-yost plugins add meta fields on the right side of the screen as soon as you open "all pages" (you can set it there without opening the page itself),
so I though the qtranslate meta fields should be there also (although no reason to think that way) :)
So now I made some progress with my website :), although I have problem with setting page title for HOME PAGE.
My home page is in fact a post with a table with prices and some text,
and I didn't set any title for this post because title and tagline are set in theme that I am using (themify theme).
By default, title of the home page is the site title but without tagline, and seo-by-yost and all-in-one-seo plugin added tagline immediately to page title.
Now I set it the way I want it in the qtranslate meta field, but I still get only site name as page title for the home page (tagline is not displayed).
What am I doing wrong? Did anybody understood my problem... :)