I've looked and looked and can not find anything that tells me how to actually enter an item into GAL. Can someone please point me to that documentation, because I certainly don't see it in the Admin Guide or by googling "gal entry" or by searching here in the forums. Everyone seems to know how to do it but me!
As long as you don't select the box 'hide from gal' a user is automatically added to it by domain (though you can change this to cross domain).
In the admin console go to domains> GAL tab and see if it's set to internal or both if you want to make use of an external LDA/AD gal (or just external only). You can also select how many results are returned by GAL searches.