@grossmsj has mostly nailed the explanation here.
The queue screen is generally about seeing what’s coming up. If Radio is picking songs for you, we give you the option to reject the next pick, or accept it and pick again. You can just sit back and let Radio pick for you, but this gives you the chance to see what’s coming up, if you’re interested.
We frequently refer to this as the “dinner party” case, where you want to line up a few hours of “pre-approved” music before your guests arrive. So you start “John Coltrane Radio” and maybe Miles Davis is perfect, but Ornette Coleman is a little too out there… Guess it depends on what kinda dinner party you’re having 
As for what’s currently playing, that’s handled on the Now Playing screen, but the thumbs only show up for music picked by Radio. We don’t give you the option to give us feedback on music you yourself picked, if that makes sense.
Finally, the heart button is for marking which tracks in your library are your favorites. The idea being that you can browse all your tracks, or just your favorites. You can play an entire album, or just your favorites. But this feature is only available in your library, so the heart will be greyed out for other content.
Hope that helps!