It’s best to start a new topic for a new issue but I’ll go ahead and answer here.
You can use a JSON string (text) or a url. If you use a JSON string, you don’t need to do an API call at all. You just convert the JSON string to an object and then use the get property of object blocks.
APIs are web-based services so you use a url to access them. I made a tutorial that explains it, especially the video: API JSON Tutorial (Video).