She was imagined either as black-haired, pale woman with fangs and claws or similar to Baba Yaga - as ugly, old witch.
As Goddess of death, her realm was Nav - realm of dead and she wasn't respected as much as her counterpart and enemy Vesna. She represented long, cold winters that could bring death of both humans and their cattle in form of starvation and freezing. Her arrival was always expected with fear, while arrival of Spring season was always celebrated.
Among Eastern Slavs, there was belief that Yarilo, when he was taken by Veles, he met Morana at the beginning of Spring and their love brought wheat and fruits. However, when Yarilo stopped liking her, she murdered him and that caused Autumn and eventually Winter to happen.
Another story says that Stribog's grandchildren - winds, bring her to Slavic realm of Yav at the end of each year, as well and Vesna at the beginning of March.
CultureIn Czech Republic, Slovakia, Russia and Poland, there is still an custom of banishing Morana that is happening around 21st of March. People would create an effigy from straw or scrap cloth, then they would beat it until dismemberment, drown it in nearby river or burn it. In Russia, that custom is called Maslenitsa.