Input.GetButton

static function GetButton (buttonName : String) : boolean

Description

Returns true while the virtual button identified by buttonName is held down.

Think auto fire - this will return true as long as the button is held down.

Use this only when implementing action like events IE: shooting a weapon.
Use Input.GetAxis for any kind of movement behaviour.

JavaScript

// Instantiates a projectile every 0.5 seconds,
// if the Fire1 button (default is Ctrl) is pressed.

var projectile : GameObject;
var fireRate : float = 0.5;
private var nextFire : float = 0.0;
function Update () {
    if (Input.GetButton ("Fire1") && Time.time > nextFire) {
        nextFire = Time.time + fireRate;
        var clone : GameObject = 
            Instantiate(projectile, transform.position, transform.rotation) as GameObject;
    }
}

using UnityEngine;
using System.Collections;

public class example : MonoBehaviour {
    public GameObject projectile;
    public float fireRate = 0.5F;
    private float nextFire = 0.0F;
    void Update() {
        if (Input.GetButton("Fire1") && Time.time > nextFire) {
            nextFire = Time.time + fireRate;
            GameObject clone = Instantiate(projectile, transform.position, transform.rotation) as GameObject as GameObject;
        }
    }
}

import UnityEngine
import System.Collections

class example(MonoBehaviour):

    public projectile as GameObject

    public fireRate as single = 0.5F

    private nextFire as single = 0.0F

    def Update():
        if Input.GetButton('Fire1') and (Time.time > nextFire):
            nextFire = (Time.time + fireRate)
            clone as GameObject = (Instantiate(projectile, transform.position, transform.rotation) as GameObject)