Module SD card help you to easily create a logging and other similar applications where it is necessary to something to save or want to resolve in a larger volume of data.
It is easily attachable as a periphery to the Arduinu.
You can read and write to the SD card using any Arduino development boards.
Build for example an MP3 player or keep long-term temperature.
Out of all the SD SPI pins: output, MOSI, SCK, MISO and CS.