What kind? Descriptions before a noun
Slowly say おもしろい本 and 便利な辞書. Point to な in the second phrase. Your first goal is simply to hear that one descriptive word comes directly before the noun while the other needs な.
1. From sentence description to noun phrase
In lesson 17, この本はおもしろいです said something about a known book. Now you can name the described object as one phrase: おもしろい本, ‘an interesting book’. The descriptive word comes before the noun. The noun phrase can then function as one unit in a larger sentence.
An い-adjective keeps its base form directly before the noun: 新しい本, いい辞書, and 安いかばん. Do not add な. With a な-adjective, な goes between the description and noun: 便利な辞書, 有名な山, and きれいなところ. The noun determines what kind of thing you are naming.
おもしろい本です。
便利な辞書です。
2. Build small, meaningful phrases first
Combine properties with nouns that make sense: いい辞書, 有名な山, にぎやかな町, and きれいなところ. One property can fit several things, but its meaning shifts with the noun. With a place, きれい can mean ‘beautiful’ or ‘clean’; the concrete situation clarifies the intended nuance.
Compare the position: 便利です ends a sentence and has no な there. 便利な辞書 puts the same word directly before 辞書 and therefore does use な. Do not write 便利なです, and do not omit な in 便利辞書 when practising this lesson pattern.
3. どんな asks for a description
どんな comes directly before a noun and means ‘what kind of …?’. どんな本ですか asks for a property or type of book. An answer such as おもしろい本です supplies exactly that kind of description. The question does not ask you to select one item from a row.
With a place, make the context explicit: ここはどんなところですか asks what kind of place ‘here’ is. A suitable answer is 静かなところです or にぎやかなところです. In この町はどんな町ですか, the town is already the topic and you ask for a description of it.
どんな本ですか。
おもしろい本です。
ここはどんなところですか。
4. Asking for a kind is not choosing an item
どんな asks for a description. どれ, taught actively in lesson 19, asks which concrete item among several options is intended. For どんな本ですか, ‘interesting’ can be a good answer; for 本はどれですか, you expect an identification such as これです.
Do not rely only on the Dutch or English wording ‘which/what kind’. Identify the missing information: a property or one object. This lesson's final check uses only どんな and noun phrases; choosing from two or more comes in the next lesson.
5. Build and check independently
Draw one description and one noun. First decide whether it is an い- or な-adjective, add な only if needed, and say the noun phrase. Then ask a どんな question that your phrase can answer. Do three rounds with a book, dictionary, and place.
The final check assesses the position of な, the type of information requested by どんな, and two bounded productions. You may write kana, kanji, or romaji. A sentence that only points out an item does not answer a question about its kind.