An attorney is a person who is licensed and qualified to practice law and represent other people on legal issues. To become an attorney, one typically has to pass the bar examination and obtain a Juris Doctor degree. Attorneys have the legal authority to do things such as write legal documents and argue cases for their clients in trials.
People often hire attorneys because legal matters can be complex, and require training and education to be dealt with properly. Also, legal matters can have serious implications for a person's life. So, people often have professional attorneys to represent them and counsel them. Attorneys work in both prosecution and defense, as well as both civil law and criminal law. Attorneys can also be appointed by the state to represent people who can't afford their own.