Tell the seller you want the gun.
Get all the sellers information. Name, address, phone number, etc...
Go get a postal money order.
Fill it out. Put it into an addressed envelope with postage.
Include a note with your name, addy, phone number, and what this money is for.
Go to the dealer. Tell him "here's everything"
He will then enclose a copy of his FFL and mail the envelope.
Seller will ship your new rifle to the FFL location listed on the FFL (your dealer)
Seller phones you when it arrives.
You go inspect, and then agree the deal is good.
Fill out the form for your background check.
Dealer calls you in, you get approved, and pay the transfer fee. (usually $25)
Go home, eat dinner, play with new toy.