These are all critical experiences that will enhance the personal, professional and educational development of the individual. You may wish to speak with a Career Counselor to help you sort it all out. Internships may be done at any time. It depends on your needs and the needs of the employer. Summer internships are usually full time, whereas fall or spring internships can be full time or as little as 8-10 hours a week during the school year.
Opportunities are always available.
What opportunities might fit your needs depends on your major, skills, financial needs, personal desires, and where you are willing to go. Positions can be found worldwide. While some internships may be available only to juniors and seniors, there are also plenty of opportunities for freshmen and sophomores. Internships are truly a case where the more the better. You will gain skills and networking contacts that can often result in permanent positions.