The printf function in the stdio.h library of C programming language is used to print formatted output to the standard output stream, which is usually the console or the terminal. It has the following syntax:

int printf(const char *format, ...);

The first argument is a string that specifies the format of the output. The format string can contain conversion specifiers that begin with the % character, which are replaced with the corresponding arguments provided to the function.

For example, the format string "Hello, %s!" contains a single conversion specifier %s that is replaced by a string argument provided to the function.

Here's an example that uses printf to print a string to the console:

#include <stdio.h>

int main() {
   char *message = "Hello, world!";
   printf("%s\n", message);
   return 0;
}

This will print the string "Hello, world!" to the console. The \n at the end of the format string is a newline character that causes the console to move to the next line after the string is printed.