SFML collisions

I'm needing help with the collision response of my player "Mario". I would like my player to be able to stand on the tiles that i add if he jumps as well as collide wit them if he walks into them i'll show the code below. I'm using AABB collision i think that's all the information that you need, but no doubt i'll miss something if you need anything more then please just ask. Thanks for taking the time to read and help out if you can.

in the game.cpp

//check collision with world
vector<Tile>* world = level.getLevel();
for (int i = 0; i < (int)world->size(); i++)
{
    if ((*world)[i].isAlive())
    {
        //if "alive" check collision
        //world tile that are not alive don't do checks
        if (checkCollision(&mario, &(*world)[i]))
        {
            mario.collisionResponse(&(*world)[i]);
        }
    }

}
 bool Game::checkCollision(MySprite* sprite, MySprite* sprite2)
 {
if (sprite->getAABB().left + sprite->getAABB().width <sprite2->getAABB().left)
    return false;
if (sprite->getAABB().left > sprite2->getAABB().left + sprite2->getAABB().width)
    return false;
if (sprite->getAABB().top + sprite->getAABB().height < sprite2->getAABB().top)
    return false;
if (sprite->getAABB().top > sprite2->getAABB().top + sprite2->getAABB().height)
    return false;

return true;

 }

in the mario.cpp

#include "Mario.h"

 Mario::Mario(sf::RenderWindow* hwnd, Input* input, const sf::Vector2f &size) : MySprite(size)
 {
scale = 200.f;
gravity = 3.5f * scale;

falling = true;
animated = true;

window = hwnd;
in = input;

walkRight.init(0, 0, 15, 21, 4, 0.3f);
walkLeft.init(0, 0, -15, 21, 4, 0.3f);
swimRight.init(0, 22, 15, 20, 3, 0.2f);
swimLeft.init(0, 22, -15, 20, 3, 0.2f);
duck.init(0, 41, 15, 20, 2, 0.6f);

currentAnimation = &walkRight; 
setTextureRect(currentAnimation->getCurrentFrame());


}
Mario::~Mario()
{

}
void Mario::update(float dt)
{
//collision with wall while jumping
if (getPosition().x < 0)
{
    velocity.x = 0;
    setPosition(0, getPosition().y);
}
else if (getPosition().x > window->getSize().x - getSize().x)
{
    velocity.x = 0;
    setPosition(window->getSize().x - getSize().x, getPosition().y);
}
if (getPosition().y < 0)
{
    velocity.y = 0;
}
else if (getPosition().y > window->getSize().y - getSize().x)
{
    velocity.y = 0;
}

//falling
if (falling)
{
    move(velocity*dt);
    velocity.y += (gravity)*dt;

}
if (getPosition().y >= 500)
{
    falling = false;
    setPosition(getPosition().x, 500);
}

if (animated == true)
{
    // ANIMATION //
    elapsedTime += dt;
    if (elapsedTime >= currentAnimation->getAniTime())
    {
        //next frame
        currentAnimation->nextFrame();
        setTextureRect(currentAnimation->getCurrentFrame());
        elapsedTime = 0;
    }
}


// INPUT //
if (in->isKeyDown(sf::Keyboard::RShift))
{
    // point to current animation 
    currentAnimation = &swimRight;
}
if (in->isKeyDown(sf::Keyboard::LShift))
{
    // point to current animation 
    currentAnimation = &swimLeft;
}

//jump
if (in->isKeyDown(sf::Keyboard::Space) && !falling)
{
    velocity.y = - 2.0f * scale;
    falling =  true;


}
/*if (in->isKeyDown(sf::Keyboard::Space)==false)
{
    falling = false;
}*/
if (in->isKeyDown(sf::Keyboard::Right))
{

    if (getPosition().x < window->getSize().x - getSize().x)
    {
        currentAnimation = &walkRight;
        velocity.x = 100;
        move(velocity.x * dt, 0);

    }
}

if (in->isKeyDown(sf::Keyboard::Left))
{
    //if (getPosition().x < window->getSize().x - getSize().x)
    //{
        velocity.x = 100;

        currentAnimation = &walkLeft;
        move(-velocity.x * dt, 0);
        //if (in->setKeyUp(sf::Keyboard::Left))
        //{
            //animated = !animated;
        //}

    //}

}
if (in->isKeyDown(sf::Keyboard::P))
{
    //in->setKeyUp(sf::Keyboard::BackSpace);
    animated = !animated;
}
updateAABB();
}

void Mario::collisionResponse(MySprite* sp)
{

//problems here
}