You’ll need to have the OKAPI URL for your Folio (more on OKAPI at okapi/guide.md at master · folio-org/okapi · GitHub) and a x-okapi-token and x-okapi-tenant defining in your http request header to interact with the APIs.
I also highly recommend joining the learning-apis channel in the Folio Slack channel (you can register for the Slack at slack-invitation.folio.org if you are not already on there)
Yes - if you look login to a Folio tenant in a browser and then look at the network tab in the developer tools of the browser you’ll be able to see the calls to the APIs that are being done to deliver the web UI