What happens if the falling star will rech the ground?

It depends, if you mean a comet or meteor, it will create a crater and will kill everything around it for about 50 km. But if you mean a real star, it is impossible because its way too big and if it comes to a distance of even a 1000 light years away, the earth will be pulled to it because of its gravity. if the earth goes of orbit like that, we'll die because it would either get too hot or too cold to live.