We have a manufacturer who has built an external configurator. I have found the following documentation on this subject:
https://developer.salesforce.com/docs/atlas.en-us.cpq_dev_plugins.meta/cpq_dev_plugins/cpq_external_config.htm

This documentation seems very limited. There is no mention of what is sent in the JSON string to the extneral configuration tool and the format it needs to be returned in. How do you utilise that JSON string that is returned to make appropriate product option selections, etc.

Does anyone have any more information or some examples?

I am fairly new to development on Salesforce (currently some clases and triggers) I have also put together a quote calculator plugin successfully and have some development background in other languages just to make clear my experience level. 

Thanks in advance.