noun
A book that explains something, such as a manual, guide, or commentary. Often used for instructional or reference works.
このソフトの解説書はとても分かりやすい。
The manual for this software is very easy to understand.
旅行の前に、
Before the trip, I read a guidebook about the area.
手引書 is a guidebook or handbook, often more practical and concise than 解説書, which can be more detailed and explanatory.
Compound of 解説 (explanation) + 書 (book).