Hello Prashant Yewate,

Mechanical engineering is the discipline that applies engineering, physics, engineering mathematics, and materials scienceprinciples to design, analyze, manufacture, and maintain mechanical systems. It is one of the oldest and broadest of the engineering disciplines.

The mechanical engineering field requires an understanding of core areas including mechanics, dynamics, thermodynamics, materials science, structural analysis, and electricity. In addition to these core principles, mechanical engineers use tools such as computer-aided design (CAD), computer-aided manufacturing (CAM), and product life cycle management to design and analyze manufacturing plants, industrial equipmentand machinery, heating and cooling systems, transport systems, aircraft, watercraft, robotics, medical devices, weapons, and others. It is the branch of engineering that involves the design, production, and operation of machinery.

Hope this will help.

Mechanical Engineering is the mother of all the engineering. It is the biggest among all the other field. 

A mechanical engineer is equipped with sound knowledge of latest technology about machine,  CNC,  automobile engine,  Turbine,  power plant,  turbomachine,  Boiller.  

Mechanical engineering deals with design and development of machine.  He is involved in maintenance of equipment.