So, for instance I don't know if the person you feed on would later become a vampire if not cured or if they are just someone you feed on. Mind shedding some light on Skyrim Vampires for me?
If you're interested ingame book http://www.imperial-library.info/content/immortal-blood is probably the best source about vampires in Elder Scrolls universe in general.
EDIT: Forgot to mention that the playable vampires in Skyrim are Cyrodiilic vampires, not Volkihar.