A manager generally makes between 15 and 20 percent of the artist's income. If you're not making an income, neither are they. If you have a manager that insists on getting paid no matter what, get out, quickly. These terms vary, according to your agreement or contract. If your manager invests money into the recording of your CD or other such things, they may ask for a larger cut.
Managers can work with a contract or without.
The terms of a contract vary, and there are no rules. Early in your career, contracts usually range in length from six months to two years. The more advanced music maker may want a longer running contract with their manager. It's all up to you, make sure you get sound advice, and references. If someone is making unrealistic promises, avoid them.