If you’re using jQuery, choose one of
$.getJSON(), then look through the requisite page in the official jQuery documentation. If you’re using native JS, look up
XMLHttpRequest() on MDN.
Also read up on CORS (cross-origin resource sharing). The easiest way to avoid CORS problems is to make sure both the API you’re using and the site hosting your page (likely Codepen) use https (or they both use http, though http is now deprecated based on consensus from security experts).
It’s true you need to read fairly widely outside of fcc, but this is just a skill you’ll need to learn in order to succeed as a developer. It’s just a shame fcc doesn’t explicitly tell students “oh, by the way, you should start researching this stuff now because we haven’t taught it yet.” I think that’s what catches people out and makes them frustrated.