When in college, you'll be presented multiple offers, so, it's important to understand what they mean!
An internship is, most commonly, a 3-to-6 month period of time where you're working for free with the aim of learning.
Your work for that company will either be (a) generalized, working cross-laterally within the company or (b) specified, working on one project until completion or the end of your contract period, whichever comes first.
Internships are incredibly helpful and should not be limited to college. They allow for failures, learnings, and so much more, without the fear of termination unless you go against your signed teams of engagement with the company.
It is common to complete 1-4 of these throughout your undergraduate and graduate degree pursuit.
A co-op is, most commonly, a 6-to-12 month period of time where you're working with pay for a company with the aim of learning or saving throughout your time in academia.
Your work is commonly focused on one project, co-ops are less generalized and you'll usually be in a specific role within the company. This role do not need to be your goal role, co-op is a time for learning, so feel free to use this as exploration. Some companies may require past experience, however, unless you're in a densely populated city with many colleges, you'll have an easier time securing a co-op than you would a full-time or part-time job.
It is common to complete 1-2 of these throughout your undergraduate and graduate degree pursuit. Co-ops are quality over quantity since you may return to this company for more formal employment in the future.