Sometimes, you may need to use the Chromebook to take a photo or a video of your work - such as graphic organizers or worksheets - and send that to your teacher. Please note that this is different from a screenshot, which is just a picture of your Chromebook's screen.
I've found these instructions and interactive tutorial at Google. Please try it and if you have problems, let me or your teacher know.
https://support.google.com/chromebook/answer/4487486?hl=en