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To the left, you have some speed buttons with search functions and a list with your previous searches. To make a new search, klick on the magnifying glass and enter your search string. Your search will be placed in the list, and the resulting files will be shown in the filelist to the right. You can jump between all your searches by selecting any previous search in the list.
If you want to specialize your search, there are several "advanced" options to choose from in he search dialog.