They are changed by getting bitten by a vampire. Then they drink the blood of the vampire. This is when they themselves begin to die. They are also buried in a shallow grave. When they emerge from the grave they are vampires and are ready to feed.
They also have a unique bond to the vampire who changed them. They can sense where the other one is and they can sense when the other one is injured or hurting.
In the True Blood series some humans like to ingest a drop of vampire blood which is called V. This has a euphoria type effect on the human and is very addicting.