why i can't see whats my friend is doings on his iphone while i am sitting next to him and i only see black black

Hi,

This is Anum Khalid from UAE. TOday my brother has gave me a challenge and if i will complete it i will got latest iPod which looks like iPhone 4. so plz help me. all i have to enable that privacy in which the other person sitting next to me can't see what i am writing n he or she will see only black light from the side and only i can see. He show me and this took three days to figure out him n he did it but now he gsave me inly two hours to figure it out plz help me...plz