Frontdesk is where you get your bag checked out. Security desk rather.
Then you can proceed to the non-air-conditioner (super hot) area where you will be directed to a window/booth where they will ask what the heck are you here for blah blah blah then you tell them to return P3. Then they may or may not yell at your fiance "why didn't you mail it in like everyone else" (uncalled for, but they just want to flex their tiny power) hahahaha. No big deal is what i'm trying to say, just brush it off and get your P3 in, ask for a reciept if possible, check if they stamp the DATE on the envelop, that will determine when your interview date gets scheduled, that how it was done in the old days.
good luck and relax.. you're moving right along the common path.