This library require the Adafruit PN532 library to work. Follow instructions at https://github.com/adafruit/Adafruit-PN532 to install the required library first. To download, click the DOWNLOADS button in the right column, rename the uncompressed folder "Amiibo". Check that the Amiibo folder contains Amiibo.cpp and Amiibo.h Place the Amiibo library folder your <arduinosketchfolder>/libraries/ folder. You may need to create the libraries subfolder if its your first library. Restart the IDE.