It can be a debacle...
First of all register with FCC by getting a CORES number. Next apply for the RTOP using the Universal Licensing System on the link from the FCC website. The forms you will need to complete are a Form 159 (provides information to them about payment being sent), and a Form 605 (the actual application). The payment code will be "RR", and the code for the Form 605 will be "PARR". Do NOT apply via US Mail, as they will probably return the application to you...I had a bad experience trying to apply this way and am still trying to get a refund of the fee that I sent the first time...long boring story that I won't get into here. Speaking of the fee, it is $50.00 and is payable via credit card over the internet. Did I say DO NOT APPLY VIA US MAIL? If you start getting at all confused, call the 1-888 number listed on the site and make them walk you through the process. It is not at all obvious what steps need to be taken, and in my humble opinion the website and entire process is the epitome of government red tape bureaucracy. Good luck...
KingAirKiddo