Assume you're looking for the word "car", but don't know in what form it may be contained in your files. It may only exist the form "automobile".
So you open the category "Science / Technical" - "Traffic" und have a look what FindWord has found there. There you might find that neither "car" nor "automobile" occurs in your files, but "pickup" instead, which you would not have thought to look for. So FindWord has helped you to find what you were looking for, without you having to type in words not contained: