When a person dies, their souls remain and if a person has done good deeds then the soul will be happy and will rest in peace, but if we have done wrong things or are restless then our soul suffers and will never rest in peace, any way good souls can be called as good spirits and evil or bad souls are called as bad spirits. Again through special invocation we can even call the spirits and they will talk to us and also will reply to all our questions and all that we want they will answer every thing. Remember while calling spirits we have to call the spirit of a good person as he will give us the right answers but an evil spirits may give wrong answers and may even harm us.