Electronic – First PIC Program using PIC16F877A and its configuration bits for Internal clock

I have a PIC16F877A and I wrote a program in MPLAB X IDE to blink a LED.

This is my program :

#include <xc.h>
#define _XTAL_FREQ 6000000
void main()
{
    TRISB7 = 0;
   while(1)
   {
         RB7=1;
      __delay_ms(1000);
          RB7=0;
       __delay_ms(1000);
   }
}

I compiled it successfully, but when I load the hex file in PICKit2v2 , it show a warning as below :

And also when I tried to write that hex file on MCU, It show the below error :

So I reopened my project in MPLAB X IDE V2.26 and tried to add configuration data to my code, using the wizard in Windows –> PIC Memory view –> Configuration Bits
But when I click it, I see this below window on the bottom of screen :

Question 1 : Why most of memory is equal to 3FFF in the first and second image that I attached above? Does that mean my program is just about 6 byte? (The first six bytes are different)

Question 2 : The error that I received is about configuration bits? Or it is something else?!

Question 3 : Which one of this optioned must I select for internal clock? I don't want to use any external clock or crystal o RC.

Question 4 : What is the difference between htc.h and xc.h libraries? I some of example code in the internet I saw htc.h included in the above of program? What is it for? Which libraries is for delay() function?

Question 5 : Is the second line in my program mandatory (I mean #define _XTAL_FREQ 6000000) Does it for external crystal? or …?

I am a brand new in PIC MCU's programming. Pleas shed any light on this issue for me and for future viewers.

Update :

I added configuration setting to my program :
Now this is my program :

/*
 * File:   newmain.c
 * Author: Amir Ebrahim
 *
 * Created on January 3, 2015, 1:42 PM
 */

#include <xc.h>
#define _XTAL_FREQ 12000000

#pragma config FOSC = HS        // Oscillator Selection bits (HS oscillator)
#pragma config WDTE = ON        // Watchdog Timer Enable bit (WDT enabled)
#pragma config PWRTE = OFF      // Power-up Timer Enable bit (PWRT disabled)
#pragma config BOREN = ON       // Brown-out Reset Enable bit (BOR enabled)
#pragma config LVP = ON         // Low-Voltage (Single-Supply) In-Circuit Serial Programming Enable bit (RB3/PGM pin has PGM function; low-voltage programming enabled)
#pragma config CPD = OFF        // Data EEPROM Memory Code Protection bit (Data EEPROM code protection off)
#pragma config WRT = OFF        // Flash Program Memory Write Enable bits (Write protection off; all program memory may be written to by EECON control)
#pragma config CP = OFF         // Flash Program Memory Code Protection bit (Code protection off)



void main()
{
    TRISB7 = 0;
   while(1)
   {
         RB7=1;
      __delay_ms(1000);
          RB7=0;
       __delay_ms(1000);
   }
}

When I load the hex file in PICKit2v2 I received successful load :

But when I want to write the file on the MCU, I receive the same previous error!

Why?! 🙁