The Now Playing Playlist shows what tracks are going to be played after the blue track already playing. In the title you can see the current track position and the total number of tracks.
You can : rearrange the tracks and move a selected one to the desired position by using the 
buttons,
remove a selected track with the 
button, shuffle the list with the 
button, and clean the playing list with the 
button.
You can rate any selected track by clicking in the rating stars.
If you Right click on a track you can see the contextual menu
from where you can...
Edit Songs this will open the selected songs in the track editor.
Edit Labels this will allow to select labels for the current selected tracks in the label editor.
Search this will allow to search a track in the list. Useful when you have many tracks in it.
Clear PlayList this will empty the playlist.
Remove selected songs this will remove the selected tracks from the playlist.
Save to Playlist this allow to save the selected tracks to a playlist.
Remove from Library this will make the selected tracks not being listed in the library anymore.
Delete from Drive this will make the selected tracks being deleted from the disk.
Randomize PlayList this will shuffle all the tracks in the playlist.
Copy To this allows you to copy the selected tracks to the directory or device you select.
Select this opens a submenu where you can select in library the Track, Album, Artist, Year or Genre of the track you are pointing at.
Select->Track if the track is not inside the current filtered view (e.g. a directory filter is active on another folder), reveal it. When the track folder doesn't match the current directory selection, select the first directory level matching the track (the deepest level already expanded in the tree) and filter by that directory instead of the track album.
Select->Album shares the track-selection navigation logic, but selects the album in the Albums Panel instead of the track in the Songs Panel. Like "Select->Track", the tree is only moved when the album is not already visible in the current filtered view, and it stops at the deepest directory level already expanded in the tree when the current directory is not part of the album path.
Select->Artist same reveal behaviour as SelectTrack: if a directory filter hides this artist (fully or partially), point the library at the artist's folder first. An artist spread across unrelated roots has no common prefix: reset to ROOT so every album stays visible instead of leaving the old (wrong) filter in place. Always reveal the artist's folder in the tree, even if the artist is already fully visible under the current filter.
Links this allows to select the link you have configured in preferences.
Commands this allows to select the command you have configured in preferences.