If you have the IPEVO document camera (the smaller grey one), use this link to install the chrome extension and launch to use. After launching, use Google Chromecast to "cast screen/window" to show what's on your display. 
IPEVO Chrome extension link

If your classroom has the AVER document camera, 
Please download either the Windows or Mac version from this site 
Avera A+ Interactive Software link
Since the VGA cables in the classroom no longer work, please be sure to connect the attached usb cable to your laptop with the program to display what's on the camera. Same as the IPEVO, please use Google Chromecast to "cast screen/window" to show what's on your display.