Implementation of headers

[Heyyo53]

I've recently been learning about command-line commands and how all that stuff works and I have gotten curious, for various of the standard headers in C++ (such as iostream, or time, etc.) are they built using these commands?

I know that there exists the std::system function that executes UNIX/Command-line commands and was just kind of wondering std::system (or something of the sort) is used to implement more system dependent actions (like creating files).

This is mainly a curiosity question as I've been kind of wondering how those libraries are implemented.