The fm:Noresults component is a virtual component, and will only be used in other components that work like a loop.
The most common example is the MediaList, in this case you can display a message when no media was found for a searchquery.
<fm:MediaList searchQuery="{$get.q}">
<fm:Loop>
<!-- template per media item goes here. -->
</fm:Loop>
<fm:NoResults>
<p>We're sorry, but your search returned no results.</p>
</fm:NoResults>
<fm:MediaList>