This Nano Ethernet Shield allows you to connect the Arduino Nano to a network. It is  assembled with long stackable pin headers, and don’t need to solder the headers separately.
The Nano Ethernet Shield is based on the ENC28J60 Ethernet chip which provide a network (IP) stack capable of both TCP and UDP. Use the Ethernet library  to write sketches which connect to the internet using the add-on module.
ENC28J60 is a 10BASE-T stand alone Ethernet unit with on board MAC & PHY, 8 Kbytes of Buffer RAM and an SPI serial interface for 3.3V and 5V logics. With a small size the Nano Ethernet Shield minimizes complexity, board space and cost. Target applications include VoIP, Industrial Automation, Building Automation, Home Control, Security and Instrumentation.
Shield use power 5V  from Nano board and convert to 3.3V (on shield have 3.3V LDO).