Important Functions - Unity 3 Game Development - page 316

Start
Start is called just before any of the Update methods are called.
Start is only called once in the lifeime of the behavior. The diference between Awake and
Start is that Start is only called if the script instance is enabled. This allows you to delay
any iniializaion code, unil it is really needed.
The Start funcion is called ater all Awake funcions on all script instances have been called.
Example
private var myLife : int;
function Start() {
myLife = 5;
}
Update
Update is called for every frame, if MonoBehaviour is enabled.
Update is the most commonly used funcion to implement any kind of game behavior.
Example
// Moves the object forward 1 meter per second
function Update () {
transform.Translate(0, 0, Time.deltaTime*1);
}
FixedUpdate
FixedUpdate is called for every fixed framerate frame, if MonoBehavior is enabled.
FixedUpdate should be used instead of Update when dealing with Rigidbody. For example,
when adding a force to a rigidbody, you have to apply the force for every fixed frame inside
FixedUpdate instead of every frame inside Update , because the physics simulaion is
carried out in discrete imesteps. The FixedUpdate funcion is called immediately before
each step.