Decide which API you wish to use. If you wish to export manually from within the desktop SketchUp application, then you can use the Ruby API.
Do you have any experience in Ruby programming ? If not you’ll first need to learn Ruby before understanding how to apply the SketchUp API, which extends core Ruby.
Secondly, you’ll need to understand how the APIs expose the SketchUp SKP model document. This only comes from much practice using the API to create model geometry and the model’s resources.
But there are some examples that come with the C SDK. If you know C, and you wish to write a standalone file converter, then perhaps the C API would be better suited to your needs.
Your forum profile mentions “SketchUp Free for Web” which does not have any “live” APIs.