just go to the counter of the airline you will use. and they will take it from there, it's really easy.
just remember to have your passport cuz they will ask. than you leave the checked bags with them, and take your carry-ons with you.
particulary o'hare. im flyin from chicago to paris in a couple of days and it's like my 1st airplane trip that i can remember. i'm flyin united so what do i do? thanks