A contract is an understanding and mutual acceptance by two parties on modalities, conduct, responsibilities and liabilities before, during and at the end of that agreed matter.
When application submitted by a person for a job is considered by the organisation and the job offer is conveyed to the prospective employee and the employee accepts the offer either by acknowledging in writing or by his action of joining that job, then a job contract has started.
Some organisations take the acceptance of the employee in a stamp paper which is executed(signed) by the employee and the authorised official of the employer organisation, quoting the job offer letter and conditions.
Job contracts may be of many pages and contain many conditions and responsibilities on the part of the employee. That will inform the employee how many days he will be on training or probation and under what circumstances his probation or training will be extended or his services will be terminated . The employer organisation will supply the employee with the code of conduct and behaviour , which the employee should comply with.
There may be a minimum service bond or a financial bond, which the employee has to honour before leaving the job.