We discover a lot about vampires in the first season episode Angel. Only direct sunlight seems to kill vampires in the Buffyverse as both Darla and Angel are able to stand in filtered sunlight. We also discover in that episode that bullets can’t kill vampires.
The belief that a vampire cannot enter one’s home unless invited dates back to the middle ages, when this was believed in eastern European. Joyce invites Darla into her home in Angel.
On the vampire itself, Giles says, “A vampire isn’t a person at all. It may have the movements, the memories, and even the personality of the person that it took over, but it’s still a demon at the core.”
Angel says, “When you become a vampire, the demon takes your body. But it doesn’t get your soul. That’s gone. No conscience, no remorse…it’s an easy way to live. You have no idea what it’s like to have done the things I’ve done, and to care.”
