The first thing  you might want to do is rename the page. For example, you may want to rename it a page from "725 Science" to "2019-2020 725 Science" so that you remember what class it was and the year.

To Rename the page, just click on the three vertical dots at the top and choose edit. Then you chance the name and any other info you want to change.

if you plan on using the same assignments as the previous year, you can choose to copy the web page. Click on the vertical dots on the tile and then choose copy.

The next picture shows what happens after you copy the webpage. You will need to rename the webpage (upper left). All the assignments are there, but none of the students or the stream is there. 

You can then click on the assignment and change it as needed. Then you can assign it.

Click where it says archive. It will be in the archive. You're done.

To find archived classes, click at the three horizontal bars on the upper left next to where it says "Google Classroom." That opens up a menu.

At the bottom of the menu, you will see where it says, "Archived classes." You can find your archived classes here. You can reinstate the archived classes, delete the archived classes or look in the archived classes here.