iTune Questions for Newbies

(I'm assuming the question is from an iTunes newbie, not intended to be answered by an iTunes noob ;-)

If a box is unchecked, iTunes will skip that track as it plays through a list. (It'll still play if double-clicked.) You can also use the checkboxes as a refinement in smart playlists ("Match only checked items").

Kind of a holdover from iTunes' early days when it was just a player for Macs; smart playlists can now do all the work of the checkboxes and more.