Scrying is a particular form of divination that can be done using a few different devices, and involves the looking into a surface, usually a clear refeltive surface, for example the crystal ball, and seeing beyound it to things that are to come. Other ways of scrying can involve using water, a mirror, the clouds, smoke from a fire.
Scrying can be one of the more difficult forms of divination to work, becuase you must altar the state of your mind in order to see past the physcial of the object used for the scry and to see beyound it, using it as a portal, you may see images, or symbols representing what is yet to come.
You should also focus on any feelings and visions you might also have during the scrying, as what you see can affect your physcial body, though some scrying causes the scryer to go in a trance like state untill the vision has ended.