This page explains the notation used for Boolean searching. You must use the 'advanced' or 'extended' search form and you must set 'match' to Boolean in the appropriate drop-down menu.
cats & dogs
cats | dogs
animals & ~dogs
(~dogs, by itself will give no results, ~ excludes results, there has to be a basic search to exclude from!)
|( )||normal grouping||example:|
(cats and dogs) or (horses and cows)