How do I make a 2D spaceship rotate to my mouse?

Hi I've been making a new game and I cant figure out how to give the player's ship gravity to slow down when coming to a stop. I also need help making it rotate to where the mouse is when i hold down the "W" Key. If anyone cant help I would be very happy to hear how to finished my character script :)

     public int MaxHealth;
     public float CurrentHealth;
     public Scrollbar HealthBar;
 
     public float MaxBoost;
     public float CurrentBoost;
     public Scrollbar BoostBar;
 
 
     public Sprite WeaponT1Image;
     public Sprite WeaponT2Image;
     public Sprite WeaponT3Image;
 
     public string[] WeaponTypeSelected = {"WeaponType1", "WeaponType2", "WeaponType3"};
     public int WeaponTypeNum;
 
     public Image WeaponImage;
 
     public KeyCode SwitchWeaponUp;
     public KeyCode SwitchWeaponDown;
 
     public float Speed;
     public float FireSpeed;
 
     public Vector3 targetPosition;
     public bool Moving;
 
     private Rigidbody2D Rb2D;
 
     void Start () {
         Rb2D = GetComponent<Rigidbody2D> ();
     }
 
     void Update () {
         BoostBar.size = CurrentBoost / MaxBoost;
         HealthBar.size = CurrentHealth / MaxHealth;
         //Player Movement
         targetPosition = Camera.main.ScreenToWorldPoint(Input.mousePosition);
 
         if(Input.GetKeyDown(KeyCode.W)){
             Moving = true;
         } else if (Input.GetKeyUp(KeyCode.W)) {
             Moving = false;
         }
 
         if (Moving == true) {
             transform.position = Vector3.MoveTowards (transform.position, targetPosition, Time.deltaTime * Speed);
         }
         //Switch Weapons
         if (Input.GetKeyDown (SwitchWeaponUp) && WeaponTypeNum != WeaponTypeSelected.Length) {
             if (WeaponTypeNum != WeaponTypeSelected.Length) {
                 WeaponTypeNum += 1;
                 WeaponImageSprite ();
             }
         } else if (Input.GetKeyDown (SwitchWeaponDown)) {
             if (WeaponTypeNum != 1) {
                 WeaponTypeNum -= 1;
                 WeaponImageSprite ();
             }
         }
     }
 
     void WeaponImageSprite () {
         if (WeaponTypeNum == 1) {
             WeaponImage.sprite = WeaponT1Image;
             WeaponImage.rectTransform.sizeDelta = new Vector2 (10, 35);
         } else if (WeaponTypeNum == 2) {
             WeaponImage.sprite = WeaponT2Image;
             WeaponImage.rectTransform.sizeDelta = new Vector2 (30, 35);
         } else if (WeaponTypeNum == 3) {
             WeaponImage.sprite = WeaponT3Image;
             WeaponImage.rectTransform.sizeDelta = new Vector2(40, 35);
         }
     }
 }