Google Classroom is a free online service that allows students and teachers to share files with each other, teachers get to post assignments for students to complete and then grade them without the need to print anything
It also helps to serve as a wonderful way of communicating, as teachers get to post announcements and also upcoming assignments, and also email both students and their parents
It also depends heavily on the use of Google Drive and a free cloud based sharing system, it allows students and teachers and many other Google services to create and store assignments