"I have an interesting book."
Translation:paq Daj vIghaj.
Klingon verb prefixes indicate not only the subject of a verb but also the object, so you usually have to use a different prefix when a verb has no object compared to when a verb does have an object.
See the "Verbs" section of the tips and notes for the first unit: https://www.duolingo.com/skill/kl/Useful-phrases/tips-and-notes
If you're using the website www.duolingo.com to learn, the tips and notes for a unit are accessible by clicking on the lightbulb after selecting the unit:
If you're using a mobile app to learn Klingon, you probably don't have access to tips and notes. I recommend not using a mobile app to learn new material (though they may be useful to review previous units where you have already read the tips and notes).
If, after reading the grammatical notes, there is still something that is unclear, please continue to ask, either in a top-level forum post in the "Klingon" section ( https://forum.duolingo.com/topic/953 ) or on an appropriate sentence discussion.
Klingon doesn't really have cases or declensions. Noun phrases work the same regardless of their grammatical part of speech.
Officially Klingon doesn't have adjectives, but there are ways to modify nouns with other nouns or with verbs in an adjectival manner. The method is slightly different depending on whether the modifier is a noun or a verb, but the simplest explanation is that a modifying noun goes before the main noun and a modifying verb goes after the main noun.
Two adjacent nouns that are not followed by a conjunction indicates a genitive relationship with the first noun indication ownership, composition, or origin of the second noun. It's possible to have a long string of nouns with only the last one being the noun actually being talked about and all the others forming various genitive relationships. I don't think we ever really explain this well in the Tips, since it can be done the same way in English. Unfortunately we start using these early in the course where we don't have any room in the Tips to add an explanation. I'll have to look for a place to add an explicit explanation.
For verbs, not all verbs can be used adjectivally. Dr. Okrand talks about a class of verbs that describes a state or quality and in The Klingon Dictionary he is pretty consistent about using "be" in the first definition of the word (like "be tall" or "be happy"). These verbs cannot take objects, so the only time one of those verbs will have a noun in front of them is when the verb is acting adjectivally on that noun. woch tlhIngan means "the Klingon is tall". tlhIngan woch means "the tall Klingon". Because this is very different than in English, we explain it in a few Tips, but the first one is in Dialogues I.
It's possible to use both at the same time: 'IH tlhIngan Duj tIn "The big Klingon ship is beautiful." I hope that helps you, but feel free to ask more questions.