This post assumes you have successfully installed the Chrome extension for Opus●Guide. If you haven't you will find the link to the Chrome store either on your home screen or under Settings in the left hand navigation bar.
In your browser, start the Opus●Guide extension. A window like this will pop up:

When ready click Start, walk through the process you want to capture in your browser and hit stop when you are finished. Opus●Guide will create the instruction, including screenshots, for you. Take a minute or two to review the instruction set - perhaps you want to rename steps or add commentary in certain parts.