Use the databases to identify possible patterns by symptoms and signs. Example: You want to find which patterns present with abdominal pain, diarrhea or loose stool, greasy tongue coat, but are definitely not a kidney or any vacuity pattern, you could enter the search parameters like this

(((diarrhea OR loose) AND patterns AND (abdomen OR abdominal)) AND (greasy)) NOT (kidney))) NOT (weak OR vacuity)

Egads. Don't despair. The search engine gives you the option to refine your search parameter by parameter each time it displays results. This is a great way to learn boolean logic, since each time you refine the search, the search engine automatically writes the entire correct boolean script, which you can then view in the find window. 

This is also a good way to search in general because searches that are too elaborate often yield too few results to be useful. I started with the very simple manageable expression:

(diarrhea OR loose) AND patterns

If I wanted to find formulas, I would have left out the word patterns and used formulas instead.  But I figured we'd start with diagnosis.  :-)