Anya was a women, living a normal life. Well, until she called upon a vengenge demon to curse her lover for using her. Then D'Hoffryn, a powerful demon saw her powerful rage, and turned her into a vengence demon for scorned women named Anyanka.
For hundreds of years she performed spells on men who had scored their lovers. A cry of a women emotionally hurt was like a siren to her. As was Cordelia's cry, when she split up with Xander
.
Cordelia decided her problems had started when Buffy arrived in Sunnydale. She made the fateful wish, that Buffy had never come to Sunnydale, and the town transforms. Giles, who hadn't been affected by the switch, found Anya's amulet (which is the source of her demon power) and destroys it, which destroys her demonic view, and turns her back into a mortal.
Anya helps out at Graduation Day, being the only one old enought to have seen an ascention before, and goes to the prom with Xander even though, as she says 'men are evil'.
She crushes on Xander, and finally in season 4 becomes his girlfriend. After asking him out because she can't get him out of her head.
Job-wise, Anya has no money, no possetions, and no clothes. Trying to fit in with the humans she accepts the money side of things and works at Giles's' newly-bought magic shop.
Xander falls in love with her, and proposes. She gets scared, because she thinks they are going to die but then accepts.
In season six, Xander keep the marrige a secret at first but then (almost) everyone is happy with the news. Anya is busy with the wedding preparation, and it doesn't give the couple time to confont their fears of marrige. And when it comes to the wedding day, of course somebody is out to wreck it. A demon, who was cursed by Anya to become a demon, spreads fears in Xander's mind and he leaves her at the altar. He wants to just go steady with her, but Anya is angry and when D'Hoffryn offers her her powers back, she takes them without thinking. She tries to get the others to curse Xander, but they've had experience with Vengance, and don't. So, seeking solace, she 'spends time' with Spike on a table top in the magic box, which hurts Xander more than any vengance.
Running the magic box on her own now that Giles has left, she was unhappy to say the least when Evil Willow wreaks it and threatens to destroy the world, starting with Jonathon and Andrew. She teleports to them, using her demon powers and casts a protection spell on them, but it doesn't hold her for long, and Willow knocks her out. Will she be able to forgive her?