Multiple Engineering Cooperative Program (MECOP) is a collaboration between a few universities in Oregon (OIT, OSU, PSU, UP) and a large number of companies to provide internships opportunities in engineering related disciplines (including CS).
MECOP is a program you apply for in the Spring before your Junior year. It is a competitive process that includes looking at your transcript, resume, and participating in an interview.
Students accepted into MECOP then go on to do two 6-month long internships, each with a different company that participates in MECOP, during their Jr and Sr years. These internships are paid - the target level is 70% of a starting salary in the field. For 6 months of full time work, this can add up to ~$20,000 or more. And once, you graduate, you will have a year's worth of professional experience, which will give you a big head start in getting your first full-time professional job.
It is definitely possible find internships outside of the MECOP program. But unless your university has its own dedicated internship program, finding those requires you finding the jobs and applying to them one by one. MECOP is an effective way to essentially apply to a large number of internships at once.
The downsides of MECOP are: you generally need part of a 5th year (1-2 extra quarters) to finish your courses as you took a term off Jr and Sr years to go be an intern; once accepted into the program, you have a limited ability to select which company you intern for (there is a matching process) - so you can't guarantee you will intern at any specific company.