Update is called every frame, if the MonoBehaviour is enabled.

Update is the most commonly used function to implement any kind of game behaviour.
	// Moves the object forward 1 meter a second

function Update () { transform.Translate(0, 0, Time.deltaTime * 1); }
using UnityEngine;
using System.Collections;

public class Example : MonoBehaviour {
    void Update() {
        transform.Translate(0, 0, Time.deltaTime * 1);
import UnityEngine
import System.Collections

public class Example(MonoBehaviour):

	def Update() as void:
		transform.Translate(0, 0, (Time.deltaTime * 1))

In order to get the elapsed time since last call to Update, use Time.deltaTime. This function is only called if the Behaviour is enabled. Override this function in order to provide your component's functionality.