The #materials method returns a collection of all of the materials in the model. But only contains that materials which already loaded to the model.
You have to use the #load method first to be able to “list” the materials.
There was an extensive discussion about it recently::
How to add all SU materials in our list? - Developers / Ruby API - SketchUp Community
Instead of putting the screenshot of your code, I would like to ask you to use this guide:
httpshow-to-post-correctly-formatted-and-colorized-code-on-the-forum
and post the code accordingly… 