IoT RedBoard ESP32 Development Board Hookup Guide
SparkFro 
Example 3: SD Card
This built-in example provides a pretty thorough demo of what can be done with Espressif's SD card library (reading/writing files, listing/making directories, etc). You'll need an SD card to get going here. Make sure you gently insert the SD Card into the SD Card slot!
To find the code, go to File > Examples, and under "Examples for ESP32 Dev Module" you'll select SD > SD_Test.
As before, make sure you've got the correct board and port selected, and upload your code.
Once your code has been uploaded, you can open a Serial Monitor to see the output. You should see something like the following (you may have to hit the reset button on your board, depending on when you opened the serial monitor):
Data will spit out to files on your SD Card. When you read the card with an SD Card Reader, you should see a couple of sample files like these!
