Hi rtell, it's good to set up a shortcut key to highlight "naked edges" which are edges that only belong to one face instead of being joined between 2 faces.

Those are the spots that need to be filled in to make a solid.

Check out here for how to set up the shortcut key:
http://moi3d.com/forum/index.php?webtag=MOI&msg=6051.2

- Michael