![10uF capacitor](https://i0.wp.com/www.exploringarduino.com/wp-content/uploads/2013/06/10uF-capacitor.jpg?resize=200%2C80&ssl=1)
Image courtesy of Newark
A capacitor is a device that stores electrical energy in an electric field. Electrolytic capacitors like this one are polarized, and are often used for decoupling purposes.
Buy a 10uF electrolytic capacitor from Amazon, Adafruit, SparkFun, or Newark.