The remote user needs to first prepare their computer to allow remote access. They can do this by going to https://remotedesktop.google.com/support. If the Get Support section has a download arrow, then they need to click that and follow the install prompts.
Person needing remote assistance & support:
After the Support App installs, you should see a Generate Code Option:
Now Click the Generate Code Button:
Copy the generated code to provide to your support agent. Then provide that code to your support agent by pasting it into Hangouts Chat, email or read it aloud (if you are on the phone) as they will need it to gain remote access to your computer