event listening of a cube and show a screen

hi

i am new to unity3D

i have created a simple game by following this tutoirl Project: Roll-a-Ball

now i would like to extend my game by

‧when the player collected all the ball and collide the cube and show a "YOU WIN!" screen and end the game

‧if the player have not collected all the ball and collide the cute and show a "YOU LOSE!" screen and contiune to play the game