Ursala sat in her lair all alone and knew that Ariel was near by, because she could hear her beautiful singing voice. She wanted it badly, as she wanted Ariel's mother's voice too.
Ursala tried her hardest to lure Ariel into in her dark cave and steal her voice many times. But hse failed because Ariel is smart and always got away.
Ariel got away one last time even after making a deal to trade her voice to Ursala. Ariel found Prince Eric and they lived happily ever after. Ursala ended up dying alone. She was cruel and didn't deserve anything but depression.