Google Classroom combines
Google Drive for assignment creation and distribution,
Google Docs, Sheets and Slides for writing,
Gmail for communication, and
Google Calendar for scheduling. Students can be invited to join a class through a private code, or be automatically imported from a school domain. Each class creates a separate folder in the respective user's Drive, where the student can submit work to be a graded by a teacher.
Mobile apps, available for
iOS and
Android devices, let users take photos and attach to assignments, share files from other apps, and access information offline. Teachers can monitor the progress for each student, and after being graded, teachers can return work, with comments. (Wikipedia)