Hi, I'm doing a course in Operating Systems and we're supposed to learn how to use pipes to transfer data between processes.

We were given this simple piece of code which demonstrates how to use pipes,but I'm having difficulty understanding it.

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>

main()
{
      int  pipefd [2], n;
      char buff[100] ;


      if( pipe( pipefd) < 0)
      {
        printf("can not create pipe \n");
      }
      printf("read fd = %d, write fd = %d \n", pipefd[0], pipefd[1]);
      if ( write (pipefd[1],"hello world\n", 12)!= 12)
      {
        printf("pipe write error \n");
      }
      if(  ( n = read ( pipefd[0] , buff, sizeof ( buff)  ) ) <= 0 )
      {
        printf("pipe read error \n");
      }
      write ( 1, buff, n ) ;
exit (0);
  }

What does the write function do? It seems to send data to the pipe and also print it to the screen (at least it seems like the second time the write function is called it does this).

Does anyone have any suggestions of good websites for learning about topics such as this, FIFO, signals, other basic linux commands used in C?