Here's how to broadcast your screen from the sending device, if it's a Windows 10 computer.
1. Open the action center.
2. Click Connect. A list of available receiving devices appears and your other computer should be on it.
3. Select the receiving device. You may have to wait a minute or longer for the devices to pair. It may also fail and you'll need to try again.
4. Toggle "Allow input" to on if you want to let the receiving device control your PC with its keyboard and mouse.
5. Click "Change projection mode" and select "Extend" from the menu that appears if you want to use the wireless display as a second desktop, rather than a mirror of your current desktop.
6. Click Disconnect when you want to terminate your connection.