The next step is to buy a firearm online, there are several websites that are wholly dedicated to selling guns, here is a list of a few of them.
If from there you want to buy a gun, then the process is simple, if you purchased a handgun the gun must be shipped from an FFL (Federal Firearms Licenced) Dealer, to an FFL Dealer. For a long gun (rifle) you can ship it from your residence to an FFL Dealer. In each case the party that is mailing the gun needs to receive a signed copy of the FFL Dealer Licence along with payment.
That's all! It may sound a little complicated but after your first purchase online it's as easy as 1-2-3.