Internships are typically 10-15 week short-term positions with organizations. Many are unpaid (government and non-profits are known for their unpaid positions, but some private organizations also don't pay). But the pay is not the main purpose -- you are there to experience the day-to-day realities of a given profession while learning the specific skills of a position within that profession. Having said this, interns are often given a lot of copies to make and other "grunt work," but you are still observing, listening, and learning.
I had incredible success with my internships -- two unpaid with the federal government and one paid with a law firm -- and secured my first job out of college based on the contacts I made at those internships. I never would have been able to get my foot in the door otherwise.
I would highly recommend pursuing internships in the field you think you want to go into during college. You might find that you love it and want to continue working toward that educational goal, or you might find that you hate it! It's all part of the process. It will help you narrow down your career goals before you spend four years and who knows how much tuition money. And just because an agency/organization/business is not advertising internships on their website, it does not mean that they would not take one on. Email or call their HR departments and offer your free labor. I did this for my first internship, and as I mentioned before, I had great success thereafter in securing full-time, paid positions!
This is also an excellent way to get satisfy the Catch 22 of needing work experience before you get your first job. Internships, so long as they are at least 15-20 hrs per week, most definitely count as professional work experience. Good luck!