One of the most common ways to program an Arduino board is using the Arduino IDE. This is a powerful tool, which allows for programming the board in C/C++. The IDE also have bulidt in compilers for most types of boards, and the newer versions also have more progrmaming tools sutch as autocompleate. For download and more information the homepage of arduino provides you with the best possible startingpoint. Here you will also find tutorials, example codes and Q/A sites with a tonn of good information.

Homepage: arduino.cc

Download IDE: arduino.cc/en/software

Intro-course: Getting Started