These are the basics about the arduino language.
Arduino programs can be divided in three main parts:
Variables are expressions that you can use in programs to store values, like e.g. sensor reading from an analog pin. They can have various types, which are described below.
Digital Pins
Analog Pins
Serial Communication
Handling Time
You can define constants in arduino, that don't take up any program memory space on the chip. Arduino defines have the same syntax as C defines:
#define constantName value
Note that the # is necessary. For example:
#define ledPin 3
The compiler will replace any mentions of ledPin with the value 3 at compile time.