What to do with form C3??

I have a couple copies of customs form C3 and am filling one out now.  My question is what do I actually do with it?  I have been planning to attach the original to Box 1 and attach copies (with a note saying original is on Box 1) on each of the other boxes.  Is that what I should do?  Or should I keep it with me?  Should I do both--attach it to the boxes and keep a copy with me in case the ones  on the boxes are lost?  The form itself says to send it to your agent, but I don't know what that would mean in the case of sending boxes USPS.

And what do I do about the "request to clear" section.  Will that be filled out by a postal worker?  I don't know the answers to those questions.  Should I sign that part or would the person filling it in sign it?

Thanks!