Static Content allows you to upload any files you'd like the Search Appliance to also host. This can be used to serve images, javascript, or CSS files that are referenced by your XSL-customized search interface.
Note that this is not meant for searchable content, which remains on the original website or file server. This is for images or files used by the search interface, rather than file contents searched by the Search Appliance.
Content will be available under the /custom/
directory, so if you
upload companyLogo.png
you can use
<img src="/custom/companyLogo.png">
in your custom search interface.