what should be done at internships?

An internship is a system of on-the-job training for white-collar and professional careers.
Generally, an internship works as an exchange of services for experience between the student and his or her employer.

The two primary types of internships
Work experience internship,
Research internship (graduation) or dissertation internship.

Refer http://en.wikipedia.org/wiki/Internship

One should try the best to get practical knowledge in the field they have,.

Practical training. For profession like medical legal, engineer internship is must.

Internship is a job before graduating. It does translate to a full time job in most cases.

Practical training is what one achieves out of an internship in addition to getting salary as part of the internship.

This is your chance to try your skills without having to worry much for result. You can always take the help of seniors with no hesitation whatsoever.

internships are on the job training. This gives an opportunity to learn more about your profession before you choose a job. They are useful for you.

Choose that area,field in which one is interested to make career for life!