should the celebrity's envelope bigger than my address's envelop? how big should the envelope be? i cant find any international reply coupons...what should i do? thnx

hi..i am new here so i have some questions ...anyone can help me....i dont understand the whole concept....how many envelopes do we send to one celebrity? how? what is self addressed stamp envelope...? :? can anyone tell me how this is done in a simple way? I am sending to David Beckham so...anyone...