Welcome to WebmasterWorld Guest from 18.104.22.168
Is there a particular reason you want to set up the filter? To get the stats for the page in real time, you can simply go to the Top Content report and enter in the page's URI in the search box. Something like, "/path/to/page.htm". This will filter the report to only show info for that page in real time.
Of course, if you do want to set up the filter, then Filter Type "Include only traffic from a subdirectory" is the way to go, with /path/to/page.htm as the parameter.