Not entirely sure of what you are askinf so I will give you the brief of Angel.
Three years before Angel started, Buffy the Vampire Slayer arrived in Sunnydale. As time went on she met some interesting people:-
Giles - Her watcher
Xander - one of her new best friends
Willow -the other new best friend
Cordelia - the school bitch with a heart of, well it was gold plated shall we say
Jenny Calendar - a teacher at her school
Faith - another Vampire Slayer that went bad
Spike - vampire with a past of killing Vampire Slayers
Darla - a Vampire in the employ of an evil fiend
Drusilla - an insane Vampire who was the lover of Spike
and Angel - a Vampire with a soul
In the first year Buffy and Angel began to form a relationship that both before and after she found out about him being a Vamp. At teh same time, Angels sire, Darla, was causing all sorts of trouble in Sunnydale making Angel have to choose(he chose Buffy).
That year progressed with Angel as a minor player as Buffy stood her ground against the darkness.
At the end of the season, Buffy died, Angel unable to save her(CPR only by the living) needed Xander.
She lived, they kissed Happily ever after - not quite.
Year two, Spike turns up with Dru. Them two, plus Darla and Angelus(Angels evil alter ego) were quite the group of vampires.
Darla sired Angel who sired Dru who sired Spike.
Through-out the first half of the year Angel and Buffy grew closer until at her Birthday he gave her the best gift of all - a good seeing to.
This was the worst thing the Vamp with Soul could have done as this caused him to revert to Angelus and join Spike and Dru.
Angelus then killed Jenny Calendar, who had become the love of Giles' life, and this obviously affected the whole gang.
After months of mental torture from Angelus, Buffy finally realized what she had to do, not before Angelus physically tortured Giles, and went to kill him.
At the same time, Willow, a fast growing Witch, was trying to restore Angels soul of which Xander was not pleased. Cordelia in this time, though her disdain for the group was showing, was actually helping them and 'dating' Xander so obviously supported him.
As Buffy and Angelus fought to the death(after Angelus was betrayed by Spike), Acathla, a demon, had been activated to make Hell on Earth. To prevent this happening, Buffy had to send Angelus to hell. Just as she was about to send the final blow, however, Willows spell worked and Angel was restored. Sadly, to save the world she had to sacrifice her love.
Buffy then ran away to LA.
Year three starts with Buffy living in LA under the name of Anne, but eventually she returns and explains that she lost Angel and that he had a soul when she killed him.
Mysteriously, Angel is returned but in a feral state as he has spent the equivalent of 100 years in a hell dimension.
Things start to return to how they were before the sex on Buffy's birthday but its becoming painfully evident that these two can't be together, yet, to all but them.
Faith, a new Slayer, arrives and in a slow decent of resentment becomes evil and joins the new big bad and tries to kill all, including the scoobies.
At the same time, her watcher, Wesley Wyndam-Price, is showing he has no use whatsoever.
The year progresses, Giles and Joyce(Buffy's mother) talk to both Angel and Buffy and explain that they may have difficulties as a couple and while Buffy as a naive 16 year old thinks nothing of it, Angel decides the best thing is to leave.
After the Big bad is defeated, Angel leaves Sunnydale.
Buffy stays.
Faith is in a Coma.
Wes is fired as a Watcher.
Cordelia leaves to become famous in LA
and the rest isn't essential.
Any questions, ask.
Anyone else want to wade in with things i've missed that are important, please do so.
I would recommend that you actually watch Buffy though.