After completing CPL and required ratings, candidates are eligible to apply for jobs as an Airline First Officer. While CPL is a generic license that provides the privilege to fly any aircraft, some type specific training is required to qualify on a certain aircraft. Small aircrafts require a very short training while big commercial jets require a Type-Rating.
Type rating is a training certification for a particular type of airplane. DGCA requires this training for aircraft above maximum weight of 5,700 kg. All turbojet-powered aircraft require a type rating, regardless of MTOW. Most of the aircrafts above this weight are generally certified for multi-crew operations, meaning it requires a captain and a first officer. Both the captain and copilot need to hold the pilot type rating for that aircraft
This training is also important because above this weight, the complexity of systems and operating procedures are very significant and beyond the scope of the CPL training skills. Most of the pilots with type-rating can only fly one type of aircraft at a time. Senior pilots with years of experience have some exemptions where they can fly 2 different type of aircrafts of same manufacturer (e.g. A320 and A330).