Open the following link in a new tab: http://tableau.github.io/webdataconnector/Simulator/. This is simulator provided by tableau to show you how accessing data from API works.
In the connector URL text field, enter the following URL: https://tableauwdc.tssapplications.com/. This is a demo url we have prepared using Digis allowing you to see a list of countries.
You can then click on 'Start interactive phase' to launch the simulation. This will fetch the tables provided by the API, in this case a table containing a list of country data. You can then fetch the data to get the list of countries in table form.