This posting is older than 6 months and can contain outdated information.
In the Library, when you tap on an item that does not have a > sign on
its right, iTunes should start playing it back immediately. The + adds
("enqueues") the track, album, etc. to your current playlist.
If you want to use choose another playlist:
1) Tap on "Library"
2) Tap on "Playlists"
3) Tap on the Playlist of your choice, so you can see the tracks it
contains
4) Tap on the track that you want playback to start at
Best regards,
Felix