Go to the throat of the world and ask for some words of power. Theyll give you a quest which points out to those and once youve read them, you can unlock them by using the dragon souls youve collected.
You can become a vampire by being attacked by one, usually can be found in snowy mountainous caves.
Or in the DLC: Dawnguard, you can join the vampire faction and become a vampire and lord. You can feed on the people in the castle, so they can be used to drop your affinity back to 1. Or buy the potions of blood which does the same.
To cure, either go to Morthal and ask the mage, which will require you a filled Black Soul Gem or do the companions guild quest and become a werewolf.