There's nothing mundane about it, but the basics... [How does one explain that to a neonate? He's never had to before.]

Vampires - Cainites, that is, after the traditional and coincidentally true assertion that the first vampire was the Biblical Cain - are functionally dead, and animated by blood, which we must consume regularly. Human blood is preferred, but animal blood will do. Without it we become dormant, that is, well, dead. Sunlight and fire cause lasting damage, and a stake through the heart immobilises, but does not destroy. The rest is - conditional upon bloodlines at times, but mostly myths that we have cultivated in order to mislead mortals. Invitation, running water, garlic, all that. Some of us do turn into bats, though. [Those were good times...]