If you are using an ipad, this is how you would easily add a photo or video to an assignment in Google Classroom:
1. Open Gmail
2. Go to Google Classroom
3. Open the class where you want to turn it in
4. Go to the assignment
5. Press on +Add or create (on the right side of the screen above the black "turn it in" button").
6. Then press FILE.
7. In the center of the box that pops up, press the grey button that says, "Select files from your device"
8. Click on "Take photo or video"
9. Take photo or video
10. Press the black "turn in" button
If your camera works on your computer, go to the camera app, take video and save.
Do 1-7 above
#8. Choose "select files from device"
9. If it is a desktop/laptop, click on Camera Roll and hit "Open" and then hit the black "turn in" button
10. If it is a Chromebook, click on Downloads, press on the file, and then hit "open" and the black "turn in" button