Explain in human language what are directives and what is a using directive?

Question

Programming

I can not understand what directives are, and why they are needed at all.

Answer 1

using System.IO connects the namespace so that the code can use it, for example, methods for reading / writing files.

Answer 2

The immediate question is, which ones? -)
using - this is at least two incarnations:
- we will use such and such a dll
- we will use this garbage only in this block, and then wipe
it out "
As applied to programming - indicating the programmer to the compiler