What level are you interested in. In the US (at least) it is typical to talk about "introductory", "upper-division", and "graduate" level texts. Introductory texts represent the first year of college instruction in physics and survey mechanics, thermal physics, and E&M in brief (the mechanics section usually covers Newton's laws, energy, and momentum). Upper division texts generally include variational mechanics and are intended for 3rd or 4th year college students

That said, authors don't write down every detail of every development: they expect readers to see some steps. How much they expect depends on the level of the text, the specified mathematical prerequisites, and the author's personality. Some texts are terse and expect a lot of the reader, others are more helpful at the cost of needing more pages to cover the same material. If you find a text completely opaque then you may need to go back and shore up your preparation a little.

dmckee‭ Usually, I am not a school, college or University student. I am interested in learning Physics. That's why I am looking for a classical mechanics book which contains most of Classical topics and, little bit of Lagrangian, GR, SR (But, It's OK if that classical Mechanics book doesn't contain this. But, Lagrangian is little bit related to Classical Mechanics so, I want that topic little bit).

I just want a book which covers most of Classical Mechanics topic (and prove theories).

@Istiak There is no need or expectation that you are in school to read a text, but publishing industry pressures drive most texts into those rough categories. The only exceptions that spring to mind are self published online (and so immune to industry pressures). But in order to recommend books to match your needs we need to know where you are in your physics journey. There simply aren't books that are good at everything or for everyone.

dmckee‭ So, I have to choose a random book which is looking good to me. If I can understand that properly then, I should move to another book. So, I have to read lots of books?