Silk icons from famfamfam.com

There isn't much functionality in the plugin, it's mostly here to avoid having multiple copies of the images from various plugins that use them.

You can reference them directly in <img> tags:

<img src='${resource(dir: 'images/icons', file: 'world.png', plugin: 'famfamfam')}'/>

but a more common use is as a CSS background image:

.icon_error {
   background-image: url('${resource(dir: 'images/icons', file: 'world.png', plugin: 'famfamfam')}');
}

Both of these can be simplified with the <fam:icon> custom tag:

<img src='${fam.icon(name: 'world')}'/>

and

.icon_error {
   background-image: url('${fam.icon(name: 'world')}');
}

Note that you don't specify the png extension when using the tag - all of the icons are PNGs so it's unnecessary.