How much does the International Reply Coupon costs and why do I need 2 of them?

Thanks

Hello,

I live outside the US and I want to send a letter to a celebrity that lives in the US, what do I need to put in the envelope and where do I put the US stamp? (in what envelope)

Thanks

Hello,

If I don't live in the US and I want to send to a celebrity in the US what do I need to put in the envelope, where I put the US stemp and what IRC stand for?

Thank you very much!