As the name suggests hacking means breaking into the secured system of either an individual or an organization.
But when we use the term " ethical", it indicates that the hacker enters the secured system of an organization with their consent, mainly to help the organization maintain proper system security against potential threats.
But sometimes hacking is done illegally to cause harm to a person or an organization, which we know as cyber crimes, which are now an offense.
A person with interest and knowledge in software, systems and hardware is eligible for a cert
Vacancies are announced by Railway Recruitment Board from time to time.
Bachelors degree with 50% is a must.
As already clarified by Meghna, these are government competitive examinations and are announced only when there is vacancy. Vacancy announcements are done in Employment News / Rojgar Samachar and are also available on Railways website.
You have to master science as a stream preferably or as per the requirement of the exam.