hi 
i d'like using this board for learning avr ... so what develop avr that is mentioned is i can programming code avr , debug without external component
thanks and best regards
That would seem to be its primary purpose.
"Debugging" with the Arduino IDE is by repetitive trials of code assembly and download. There is no hardware "debugger" but that is in any case rarely appropriate.
so , that meaning we can't write code like as avr ( using library atmel , compiler GCC ...) or ....
The Arduino IDE allows you to write code in C(+ - whatever) which it assembles using GCC and then uploads to the Arduino using serial communication via USB to a bootloader pre-programmed into the Arduino MCU.
You can insert assembler code if you like.