When you're just starting out, your manager will wear many hats. A manager has to be a cheerleader, psychiatrist, advisor, guide, problem solver, and what I affectionatly refer to as babysitter. This means YOU still make your own decisions, your manager will advise you, but you still need to take responsibility for your career. A personal manager will also help you decide which record company to go with, what publisher to use, and when you should go on tour. They are also your creativity manager, helping to choose the right songs, producers, and musicians if needed.
Managers handle all requests for time and money, and fight off blood sucking users.
There are a ton of people just waiting for the latest talent to hitch a ride with. It was MC Hammer's blood sucking entourage that made him penniless, not his lack of work in recent years. Managers can sometimes act as a booking agent. An agent books shows for an artist, but their loyalty is to the place they are booking you in, not to you. Some states, like California, limit a manager's power by not allowing them to book shows for their clients, so you need to get advice in that area.