You can set Simple Search Options from this tab.
Please see Simple Search for explanation on simple search operation.
You can choose whether the simple search is going to be applied for All Metadata Fields , or Over Specified Fields.
-For Specified Fields, after clicking Add button , you can select the fields for your preference among the All Fields list.
You have the option to make all search operations based on full-text match. Please see Simple Search for information on full-text / partial match options.