You can start typing your search words in this text box. You can also perform an "empty" search, without keywords, by simply clicking the magnifying glass. 

If the search option "search suggest" is enabled, you will see a list of keywords appear as soon as you start typing. The keyword list shows only keywords that are in your index. 

If the keyword is in the list, you can select it and perform the search query. 

You can use wildcards (*), but not at the beginning of the word. A "?" is a single character wildcard. You can do a phrase search by using quotes (i.e. "church bells"). 

Clicking the arrow button in the search text box opens the advanced search screen.