What methods should I call in the GPT API to get what I need?

In my current scenario I will need to do the following:

1 - Send a list of documents in HTML.
These documents have instructions for the user to carry out operations in their work.
2 - The user will, for example, ask the API “How do I make a sale in my ERP and register a user as a customer”.
The API responds based on the original document the step by step described in the original document.