Can someone explain me exactly what the below definition means in the C standard about directives

Question

What i exactly need to know is what characters are allowed before the start of a directive as we all know we can have new line characters and whites

Answer 1

What this all basically means is that either # is at the start of a line or there is only whitespace before # on a given line.

This part:

either the first character in the source file (optionally after white space containing no new-line characters)

Allows for whitespace before # if it's on the first line of the file, while this part:

or that follows white space containing at least one new-line character.

Allows for whitespace before # on any subsequent line.

For example:

  #include <stdio.h>   // spaces before the first line
  #include <stdlib.h>  // spaces before another line, i.e, spaces and newline before a token
int x;   #include <string.h> // not allowed, other tokens preceed on same line