This is the 3229th most frequent Russian word.
нужный
Needed; necessary.
Here, 'нужную' is used as an adjective modifying 'книгу', emphasizing its necessity or relevance for the exam.
Я купил нужную книгу для экзамена.
I bought the necessary book for the exam.
In this sentence, 'нужных' refers to the type of people suitable or required for the project.
Для этого проекта важно найти нужных людей.
For this project, it is important to find the right people.
Here, 'нужными' describes 'советами', indicating the advice provided is relevant or needed.