A dialog window shown below is used to set or edit word-based filter. Since word-filters are specifically designed to check occurances of words, first you have to add those special words by typing into the 'New Keyword' field and clicking 'Add Keyword' button.
Sample screenshot above shows a filter definition of virtual channel filter. Shown definition tells that it is looking for two words, namely 'NASA' and 'Mars' in the post. If it finds one of them, that post is moved into its associated virtual channel.
More Options to Tune Filter
If you like to tune your filter for better filtering experience, you can click 'More Options' button located at the bottom-left corner of the dialog, which expands the same window to let you to see following settings panel.
Sample screenshot above shows default settings for given filter definition above. Thru these extra settings, you can make filter check certain fields in the post, or change its behaviour from Filter-in to Filter-out, or make sure post satisfies only if that post includes all filtered words at the same time.
To learn more about from where filters can be defined for a channel or virtual channel, check out related help topics.