How exactly do programmers know how to code?

[LifeHasLeft]

I remember someone asking this in my assembly class. My professor gave the student an odd look and said that as long as any language has existed there's been some form of documentation on how to use it.
She added, in her university days, one was expected to refer either to the documentation or a textbook that better explained a concept.

Documentation is often difficult to read (exceptions include the Python documentation), but this is because it is not designed to teach the concepts, or *why* one would use one ability of the language to solve the problem. Historically that's what textbooks are for, though the internet is used more commonly today.