You can also go the 9v battery route plugged into the on-board regulator of the Arduino but the low mAh rating of a 9v won’t allow your project to stay running for very long.

Powering the prototype up through the USB port of your computer is not recommended. You will also need a USB power supply and the Arduino Uno R3 USB cable, or a 9V Li-ion battery and one Arduino 9V ...