Heaven is a supposed location that is perfectly peaceful, joyful, and perfect.
In popular imagination heaven is entered through the pearly gates. In heaven, people sit on clouds alongside angels and play harps. Only good people go to heaven. Bad people go to hell. Most people when they get to heaven seek out their loved ones.
Whether or not pets go to heaven is unknown. Many people like to think that when they get to heaven they can be together with their lost pets.