Most tracks you play will most likely appear in the Playlist, which has two views: the List and Grid.
Change between List and Grid views at any time by selecting the appropriate tab.
In the list of tracks, left click to select a track. Move items by dragging them up or down. Remove a track by dragging it back to the Library. When playing, the End Time column shows the time the track will finish.
Use the Play button to play the currently selected track, the Pause button to pause (click Play to resume) and the Stop button to stop the track. The indicator at the bottom displays progress of the currently selected track while playing - move the indicator at any time to go to a different part of the track.
When a track is playing, you will not be able to select another track (however you can play multiple tracks in the Grid view). Tracks in the Playlist do not need to be in the order you intend to play them.
When you right click a track in the List view you get a short menu of options for the currently selected track, including removing it from the Playlist, moving it up or down and displaying additional information about the track.