if you go to this page in a browser, you get redirected to documentation for the v1 API, which in turn links to https://www.inaturalist.org/pages/developers, which in turn links to https://www.inaturalist.org/pages/api+recommended+practices.
you should read through all of these pages. they answer your question and also provides suggestions for other ways to get observation data.
after reading these pages, if you still think you need to get information from the API and still aren’t sure how to get what you need, please describe why you need to go through the API, what you’re trying to accomplish, and which language / tool you’re using to interact with the API.