Arduino is the Open Source Electronics Prototyping Platform that has taken the Maker Movement by storm.
To use the introductory examples in this guide, all you need is an Arduino Uno or Leonardo, along with a USB cable.
From obtaining the required components to putting the final touches on your project, all the information you need is here Getting Started with Arduino is a snap.
This thorough introduction, updated for the latest Arduino release, helps you start Prototyping right away.
Arduino is the Open Source Electronics Prototyping Platform that has taken the Maker Movement by storm