Under File List's Discovery Type, you will be required to enter a file location containing a URL list (one item per line):

Once done, click on "Start Test" button to initiate session.

Important Note: File format must include one URL per line. You may use a full extension URL (followed by a URI if necessary). If a protocol is supressed (e.g: "http://"), N-Stalker will consider a clear text HTTP connection ("http://").