Hi dear,
        Diploma in mechanical engineering is a 3 years long Diploma certificate program.This course can be pursued by students who have passed 10th class.
Some of the important topics covered in this branch of engineering include- material science, engineering physics, theory of machines, kinematics of machines, thermodynamics, manufacturing etc. With development in technology, new topics have also been introduced, like- CADD (Computer Aided Design and Drawing), nanotechnology, mechatronics etc.
This branch deals with design, manufacturing and operation of machinery.
Feel free to ask further queries in comment section.
Hope this helps!!