If you are searching using "All", then each term in your search must be matched in the results. If you are searching using "Any", any single term in your search string will produce a match.

If you decide to use "Logical AND/OR" as your search method, you can enter multiple search terms separated by the words "AND" and "OR", and can group terms using parentheses.
Acceptable search syntax:

ellison AND oracle
gates OR monopoly
(gates OR ellison) AND billionaire
windows AND (crash OR bsod) NOT macintosh