On the machine you are trying to connect to open the Chrome Remote Desktop Software
Click the Share My Screen button (it may appear in white depending on how your computer is setup, you may be prompted to login with your Google credentials.
Click the blue + Generate Code button under Share this screen
The system should generate a temporary code that can be used to allow a remote session.
Now back on the computer you would like to connect from, open Chrome Remote Desktop App
Click on the Access code field in the Connect to another computer section and enter the code provided by the remote user. Note: Codes change every 5 minutes. Sometimes you may get disconnected from the remote computer and you may need to enter a new code.