Operators are used to do various types of operations with expressions. An expression can be thought of as being manipulations of variables. Check out more on operators in this Wikipedia page.
Constants are variables whose value when once initialised, cannot be changed afterwards.
They can be written like this:
const <data_type> <variable_name> = <initialised_value>;
They can be used almost everywhere a normal constant is used. (But you have to be very careful about it and there is a proper syntax. I might do it in a later tutorial series.
A library is a collection of classes and functions which can be used to make programs faster, something like the modules of Python. The main library of C++ is called the STL, or the Standard Template Library. It contains a lot of classes and functions, and almost all C++ learners will eventually learn it. It is also a work in progrss, constantly updating itself (The latest update was in 2017).
This is the end of “A Beginner’s Guide to C++”. I will still try to post new information every day, but it will probably be problems, becuase that’s what I have been doing now.