WeVideo is a powerful, web-based video editor and our school maintains a subscription with this service.
You should probably have received an email from your teacher inviting you to join. Use that link and log in using your school Google account.
This is Justin Brown. He does a great job walking through the options WeVideo has:
If the Google Drive app is on your phone, you can load the video on whatever app you used to record the video and look for a "Share" button. You should have an option to send the video to Google Drive.
Start by recording your video:
Next, we make sure Google Drive is an option to share: