Maybe others will disagree, but I don't think Llama Index is a good place to start unless you know exactly what llama index is and what it offers. I would personally watch this video:
https://www.youtube.com/watch?v=jkrNMKz9pWUThis short course is also similar:
https://www.deeplearning.ai/short-courses/building-systems-with-chatgpt/I would start this by learning about using the llm apis, and once you've learned the basics of that, a framework might make sense for the direction you go
