Differences between "How to Use OpenAI API for Q&A and Chatbot Apps" and the Fine-Tunning?

Hello.
It’s not clear for me the differences between the documentation describing “How to Use OpenAI API for Q&A and Chatbot Apps” and the Fine-Tunning…

At the end of the day both seems to address the same use case. Or not? Could someone, please, make me this more clear?

Cheers!