This feature must first be enabled for your teachers in the Device Console > Organization > Settings > Permissions tab > in the Teacher Tools section > Save

1. Start a class on Teacher Tools.
2. Select the student(s) (if you are just sharing with a group and not the whole class) you want to share with.
3. Click on the Share screen button.
4. Answer the prompt about whether or not you want to lock students into a shared screen, and the prompt to allow audio to be shared.
5. Select the Screen, Application Window, or Chrome tab that you wish to share.
6. Click the Share button. 

7. To stop screen sharing, click the Stop share screen button.