Your list of assigned homework can be found in two places within Google Classroom
First on the Stream page near the bottom
Second, by clicking on the "Classwork" tab near the top of the page
Click on whichever assignment you're needing to work on
Click on "View Assignment"
Click on "Add or create" near the right to open a drop-down menu
Click on Google Drive, if you have already done the work
Click on Docs, Slides, etc to create a new, appropriate file for the assignment
When you are done with the work, click on the "Turn in" button