You may either enter your search criteria in one or more fields or leave all the fields blank.
In the latter case, no restrictions are applied, except those defined by the search options on the Simple search page and the Advanced search page.

A logical AND will always operate between your search criteria in the different fields.

Example: specifying a from date of October 2010 as "from date" and "Lending" as "Main Topic" will return all documents both dated between "October 2010" and now and having "Lending" as "Main Topic".