A crystal ball is used as a form of scrying and goes back centuries first utilized by the Druids. A crystal ball has always been associated with witches, psychics and gypsies but also has a strong base in religions all over the world. It is used as a form of fortune telling as other tools such as black mirrors, flames, clouds, pools of liquid. Gazing into any of these tools is called scrying and scrying is why diviners are called seers. All of these practices are a form of fortune telling which is now practiced all around the world. In Old Europe one superstition was on Hallow's Eve for a single woman to turn out the lights and light one candle and gaze into a crystal ball or mirror and she would see her future husband.
The true scrying tool is your own mind. Each of the tools I have mentioned here allows you to focus more intently. While most of us use only 10% of our brain, utilizing a tool such as these taps into your subconscious allowing you to seek deeper than usual. Same is with your dreams, they are symbolic, as are the images you conjure from your scrying. Pay close attention to what you see, why you are seeing it and listen to the message you are sending to yourself, as you are in control of your future and with scrying you manifest it with your mind.