If you're trying to share an assignment in Google Classroom and it doesn't seem to be working, this might be due to filters from your browser. Look to see if there's a red "X" on the right side of your browser search bar. If there is, click on it and select "Always allow pop-ups."
Here are several articles to explain how to enable pop-ups on:
Google Chrome: https://support.google.com/chrome/answer/95472?hl=en
If pop-ups aren't being blocked and you're still having this issue, please contact us at firstname.lastname@example.org and we'll look into the issue for you!