How does coding for Arduino work?
Basically you will write a bunch of instructions on your computer, upload it to the Arduino and then it runs on an endless loop, waiting for an input from sensors or executing what you told it to do.
The easiest way to get started is to head over to arduino.cc and work yourself through the Basics. They are well-written and every component or function used in the examples are referenced at the bottom so you can look up again what they mean.