Tara appears in the middle of season 4 when she meets Willow at the college Wicca meeting. Willow and her are the only serious practicing Wiccas. Willow had just broke up with Oz and was really depressed, since he had moved away so he wouldn't hurt her. When Oz finally came back, Tara and Willow already were a couple. He hated Tara for doing that to him and almost killed her when he turned into a werewolf. Luckily, Buffy came and was able to stop him.
   Tara taught Willow a lot of witchcraft and they're both very talented witches. In the middle of season 5 Tara goes insane because of Glory, a Hellmouth god. In the end of season 5 Willow is finally able to bring her back to sane.