Explain how I can use an API to pull data via a userscript ran by tampermonkey.  Can you provide me the documentation and links? 

What I want to use this for is to add text from an API into a textarea on the site "https://chat.openai.com/chat". 

How do I debug this, and what is debugging?

Oh, and include a list of 5 free apis I can use to get data.