(a) whats a generator, and why should I care about them?
Generator is an internal mechanism responsible for creating either service or a route. You usually don't care about them as stated in the doc.
(b) where is the information on the "port" flag. The Redhat provided course material I'm taking says that it exists. Is there a place where the syntax is more comprehensively documented?
In most cases oc expose is smart enough to read that information when needed, but in those rare cases where it fails it'll tell you to provide
the --port flag. You can always get more information about any command with --help flag, like oc expose --help