1. Drink the blood of a vampire. 2. Die (I know, it sounds counterproductive, but you will come back. 3. Drink the blood of a human. And TADA! You are a vampire!
You cannot die! Kind of! You will not age and cannot be killed, unless you are stabbed in the heart with a wooden stake, bitten by a werewolf, go out in the sun without a daylight ring, or by fire.
You must drink vampire blood to survive. If you do not, you will eventually desiccate and turn to a statue-esque thing. However if you are fed human blood again you can be revived.
Pretty much everyone in Mystic Falls. Caroline was turned early on by Katherine Pierce to send a message, but she actually ended up way better off as a vampire anyways. She learned to drink from a blood bag and handle impulses, but others aren’t quite so lucky.