Mostly spells are used for to heal, to protect, to attract something for personal gain or the common good, to discern past events, present influences, and future probabilities, to conceal things that should remain secret or save from harm and to repel negative onslaught. It is recommended by all Witches that you read alot of books on how and why magic works. Remember practice makes perfect. For example if you have hung a horseshoe over your door or had a rabbits foot for good luck you have cast a luck spell. This is also goes as far as wishing on a shooting star.
Whether we know it or not since ancient times spells like this or any superstitions like these have been going on for thousands of years in all human cultures. It is good to study other cultures and their magical practices along with how the dominant Western culture has endangered traditional magical practices by denying their validity. Magic has long been reviewed as a threat to the dominance of religion and later, of science, although it is the parent of both of them and the bridge between them.
The Romans and other ancient rulers consultated Oracles who observed and heeded omens, and interpreted dreams before commencing wars or other complex affairs of state. Merchants did the same thing before going on a voyage or caravan. Even the Bible has examples of this.