This is the 4523rd most frequent German word.
nützlich
Useful.
Here, 'nützlich' is an adjective describing the book as being beneficial or helpful for a specific purpose (research).
Das Buch ist sehr nützlich für meine Recherche.
The book is very useful for my research.
'Nützlich' is used to describe the practical value of having a flashlight during a hike for enabling a safer and smoother experience.
Es ist nützlich, eine Taschenlampe auf der Wanderung mitzunehmen.
It is useful to take a flashlight on the hike.
In this example, 'nützlich' characterizes the tips as instrumental in achieving effective preparation for an exam.