-on which pin R1 or R2 I have to connect signal I do not need max232

PIN7 (RB1) is input, Pin8 (RB2) is output, with an arduino or PIC/AVR you do not need a MAX232.

Eg. an arduino sends info to pin7 (RB1)

--------------------------------------------
-what is purpose of these push buttons

These buttons may be used as serial buttons.
Then you need only 2wires from de arduino/pic/avr.

Each push button sends a code via pin8 (RB2) to the arduino/PIC/AVR who can then process this code.
Button1 sends the ascii code A
Button2 = 'B'
Button3 = 'C'
Button4 = 'D'

Button5 = 'E' (optional)

You are not obliged to place the push buttons, without the buttons the LCD display works equally well.
----------------------------------------------------

-what is purpose MCLR do we need it or not.

The MCRL is the Reset/programming input but can also be used as an IO port.
Ihor has modified the program so you can use 5 buttons with the MCRL input and then send the ascii 'E' to the arduino / pic / avr.

----------------------------------------------------
-which are command for home and new line position

Cls + home = /0x58

cursor position (command, column, row) = /0x47/0x01/0x01