This is an Arduino Nano I/O expansion board.  Your Arduino Nano fits directly into the headers on this board.  This board is designed to quickly and easily provide for connection between an Arduino Nano and any component you would like to add.  This board includes a DC barrel jack for easy connection of a wall power supply.  It also includes a reset button.  This is the perfect accessory to make your Arduino Nano prototyping much easier and trouble free.