An employment contract is an agreement between an employer and employee about the employment relationship. There are no legal requirements about what must go into an employment contract. Typical contract provisions cover topics like compensation, benefits, start date, job title and responsibiltiies, and termination provisions.
Some employers use contracts to confirm (and create proof, if it becomes necessary in the future) that an employee works at will (that is, that the employee can quit or be fired at any time, for any reason that's not illegal). Some employers give up their right to fire at will in an employment contract, in exchange for the employee's agreement to stay with the company for a set length of time.
This section covers common types of employment contracts and contract provisions.