Giles' assertion that he doesn't have an instruction manual is not strictly true. There is a Slayer Handbook, but Giles just decided not to use it with Buffy.
The episode was alternately titled "The Anointed".
"Here endeth the lesson" comes from many Christian denominations, when the lector finishes reading the scripture lesson, they often say "Here endeth the lesson".
Owen was initially named "Chambers," as he was identified in the original script.