Sir/mam I am willing to do internship in DRDO during December month. So how I can apply.plzz respond ramyavepuri16[at]gmail.com

There is a list of labs that fall under DRDO. Have a look at them. Many of them require student interns for their projects.(both bachelor and masters).

The procedure after this depends on your preferred field of work. In my case, I wanted to work in Computer Vision/Artificial Intelligence. So I decided to apply to Centre for Artificial Intelligence and Robotics, Bangalore for a 6 months project.(Note that not many labs allow a 2 months project, because it neither does justice to you nor the lab.You hardly achieve anything with such a short stay).

Once you have decide upon the field/lab, make a short resume and a cover letter describing why do you want to apply TO THAT SPECIFIC LAB (very important), the work you have done/are doing in the field if any and what you want to achieve with your stay there.

Make a google document of these and send the page link to the director of the lab
Please don't add attachments, they generally end up in spam.
Don't leave your mail blank. Give proper subject and details

The director forwards it to Additional Director(Training), who is the incharge of handling student/project trainee related issues. (I think you could even mail it directly to AD(Trg) )

After that you need to be patient. In my case, I got a telephone call, had a short interview/discussion about my interests, academic background, the project I had done in Computer Vision and the work that the scientist I would be allotted was doing. They asked for my most current resume with the courses I had done and all. They also, in many cases, ask for a letter from your HoD, stating that you are allowed to work/intern outside college for 6 months.

Once they have your letter and resume, they discuss and decide whether you are to be selected, in which case, dates are decided upon and your final acceptance letter is sent to you.