Font Awesome

[ZuluPilgrim]

From the documentation using Font Awesome seems to be easy but when I try I get a broken image.

E.g. https://fontawesome.com/icons/book?f=classic&s=solid is reference in ccs as
<i class="fa-solid fa-book"></i>

The name is fa-book but how do I work out what the category is? I can't find a reference to it anywhere on the page (or I am looking in the wrong place).