Collision detection c++ and boundry detection

I am making a game where the player uses the arrow keys to control a submarine to avoid obstacles. However I am unsure of to detect collisions between the 2 objects...

Using c++ and SFML I have declared the Submarine sprite like this

public:
      void Submarine::Init(const std::string& ImageFile)
{
      cout<<"Sub loaded";
      submarine.LoadFromFile(ImageFile);
      cout<<"Sub stored"<<endl;
      subSprite.SetImage(submarine);
      subSprite.SetPosition(150,300);
      subSprite.Scale(2.0,2.0);
}

and the obstacle sprites are declared like this

class ObstacleSprite : public Sprite
{
public:
      ObstacleSprite();
      ObstacleSprite(const Image &Img, const Vector2f &Position=Vector2f(0, 0), const Vector2f &Scale=Vector2f(1, 1), float Rotation=0.f, const Color &Col=Color(255, 255, 255, 255),float scrollPos=0.0);
      void setScrollPos(float scrollPos);
      void setVertPos(float vertPos);
      float getVertPos(void);
      float getScrollPos(void);
}

My best guess is a bounding box, but as i've never written one before I am unsure how to go about it. In the SFML documentation there may be somthing like 'get sub rect' but again I am unsure how to implement these...

This is a link to sf::sprite documentation
http://www.sfml-dev.org/documentation/1.6/classsf_1_1Sprite.htm