Internships provide supervised practical experience at a company.  When you are hired by a company you are assigned a mentor who’ll be your supervisor for your internship (generally during the summer).  The program provides a combination of learning and practical experience.  Although most internships are filled by college students, a few may be offered to teens who are graduating high school seniors, and fewer still to underclassman.  Some are paid, although generally at a minimum salary, since the company teaches you skills and allows you to gain experience in the field.  As an intern, be prepared to do a fair amount of busy work from filing to copying, even doing errands.  The highest paid internships are generally awarded to graduate students, like law students, whose internships become part of the recruitment process.