The group of spells known as fortune spells can do two things. First they can perceive a future, and thus act as fortune telling tools. Secondly they can change and manipulate fortunes and futures.
The power of fortunes lays in the power of the magical forces which control all magic. The more powerful this magic force is within the caster the easier it is for the caster to manipulate fortunes and the more detailed fortuntelling can become.