These are platforms that allow you to apply to multiple schools with a single, standardized application. Instead of filling out multiple applications, you fill out one application that you can submit to each college. Compare your college list to the schools that accept each application to decide which one(s) might be right for you.
Remember that you'll still need to pay each school's application fees, and some schools may require additional materials. Speak with your school counselor if you need college application fee waivers to cover this expense.