There is a micro SD card slot on the board. This slot adds data logging capabilities to the system.
The slot is a push-pull style which eliminates external card eject.
CLK: SCK (D9).
CMD: MOSI (D8).
DAT0: MISO (D10).
CD_DAT3: CS (D4).
POWER: VCC (+3.3V) and GND.
Arduino IDE includes an SD library by default to access and modify the file system.
There are few examples located in the File > Examples > SD menu.