Kiten's most basic mode is as a dictionary for looking up both English and Japanese words. You can also add other dictionaries to Kiten's list.
To look up words in either language, type them in to the text-edit (much like Konqueror's location bar) and press either Enter or the Search button on the toolbar (again, much like Konqueror). Kiten will then look up the word.
You can enter Kanji, Kana and English and get back results from Kiten. These results of your search will appear in the large results view which takes up the majority of the Kiten window.
Often times you will want to filter rare words from your search. Kiten will do this for you if toggle Settings->Filter Rare.
Not all dictionary files support filtering rare entries - most dictionaries, excluding the two provided by default in Kiten do not.
If you have not enabled filtering rare entries, common entries will be labeled Common in the result view.