In order to share your desktop you will need a streaming software with screen capture capability.
Some recommended tools are:
- OBS Studio: https://obsproject.com/ (Windows + Mac, Free)
- Wirecast: https://www.telestream.net/wirecast/overview.htm
- ManyCam: https://manycam.com/ (Windows + Mac)
- Ecamm Live: https://www.ecamm.com/mac/ecammlive/ (Mac)