Buffy is still no longer a cheerleader, but she is the new girl at Sunndale High. Giles, the librarian, is her mentor. Xander and Willow are her friends, known as the Scooby Gang. Angel is a vampire, and he is cursed to never have true love. Spike is a bad boy turned good. These are the main characters. There are so many other good people on the show, but you need to watch it to find out!
Angel is a spin-off of Buffy. Angel moves to Los Angeles and becomes the head of a Wolfram and Hart Law office, which is run by mythical Senior partners. (This is a long story that's explained in the show). Gunn, Wesley, and a variety of other characters make this a memorable and equally interesting series. The episodes run in tandem with Buffy, and in my opinion, was cancelled too soon.
Buffy and Angel live on in a comic book form. I suggest watching the show before picking up the comic! It's excellent!