You can submit an assignment in Google Classroom under the "Classwork" section on the desktop site or mobile app.

I walk through how I set up and use Google Classroom to make teaching easier and more organized. I show how to create a class, invite students using a class code or email, and share assignments ...

Google built Google Classroom, its free education platform, to help teachers create assignments and simplify the distribution and grading process.

Google’s launch of Classroom last year was a natural next step for that. Now, with more than 50 apps integrating with Classroom, Google is making the service more extensible.