Actually the Play Now settings guide helped, thanks.
However, the queue next function adds that song to the playlist, basically making a duplicate instead of playing existing one. It's kind of difficult for me to explain it in English but hmm.
Let's imagine I have a playlist of songs names of which are numbers from 1 to 5. There is no shuffle enabled. Right now song '2' is playing. I'm using Artist Artwork to find a song '4'. I'm double clicking it and instead of playing song '4' in my original playlist of 5 songs, it creates another 'now playing' with just song '4'. If I use queue next option, it adds another song '4' to my 1-5 playlist, and makes it so that there are 2 songs '4' there now.