NCERT books lay the foundation for an individual to know the concepts and fundamentals of physics, chemistry and mathematics and that is why they are recommended by a number of people to those candidates who are aspiring to appear in the engineering entrance examinations. Once your basic concepts and fundamentals are clear, then you can study from the next level of books and understand them better. For Example, questions in the JEE Main exams are mostly based on the topics from the NCERT books. After you go through the NCERT books thoroughly, may be you can explore solving question papers of past years of JEE and other engineering entrance exam. This will help you analyse why the NCERT books are recommended by majority of people.