putting jump in project#00

can anyone help me with my code i'm new to this. i'm trying to put a jump command in the code for project#00. i works with a few problems. the gravity is affecting the speed and when i hold space the sphere keeps jumping.

using UnityEngine; using System.Collections;

  public class MoveAndJump : MonoBehaviour

  {

  public float jump = 8.0f;

  public float gravity = 20.0f;

  public float speed;     public GUIText countText;     public GUIText

winText; private int count;
private Vector3 moveDirection = Vector3.zero; private bool grounded = true; void start () { count = 0; SetCountText (); winText.text = ""; } void FixedUpdate () { float moveHorizontal = Input.GetAxis("Horizontal"); float moveVertical = Input.GetAxis("Vertical");

  Vector3 movement = new Vector3(moveHorizontal,

moveDirection.y, moveVertical);

  rigidbody.AddForce(movement * speed * Time.deltaTime);

      if (grounded)

      {

          if(Input.GetButton ("Jump"))

              moveDirection.y = jump;

           }

                //Applying gravity to the controller

      moveDirection.y -= gravity * Time.deltaTime;

      }

  void OnTriggerEnter(Collider other)      {         if(other.gameObject.tag

== "PickUp") { other.gameObject.SetActive(false); count = count + 1; SetCountText (); } }

  void SetCountText ()     {         countText.text = "Count: " +

count.ToString(); if(count >=12) { winText.text = "YOU WIN"; } } }