You've got the stuff.
When you download content from the nuken Shop, it's automatically installed to the correct location in the
content/directory. After you relaunch nuken, your content will appear in the Downloaded Content Menu.
From this area, you can view where your content is installed directly (in your default file explorer).
content/addons- Where add-ons get installed. If you have additional
.jsadd-on files you'd like nuken to run, drop them here.
content/themes- Where all themes get installed. If you have additional
.csstheme files you'd like to apply, you can drop them here.
content/templates- Where templates get installed. You can drop your custom template files here in this directory if you'd like. Just make sure to relaunch nuken afterwards.
The Downloaded Content Menu has two more sections you might find interesting.
Detected content - All detected nuken content (content that's been set up in a way nuken can parse and understand) will show up here. If you'd like to delete an item displayed here, see the section below and delete the file itself.
All detected files - Regardless of whether it's official / detected nuken content, all files nuken runs show up here. You can view the file directly, or even delete it.