Most likely you already have an account as that's needed to register with FAA. This is after all FAA's own site.Dronezone: FAADroneZone
Create an account, find the location where you want to fly and fill out the request. Takes anywhere from a day to week to hear back. Don't do it on a Friday or before a holiday. Do it early in the week. Also, you can put in for an extended time (I usually go for a year).