I used Apps "DTV : Destination Thailand Visa" Read all about DTV Condition. and after that I decide to let them do it instead I apply myself, just if you can understand all details you also can apply by yourself 😉
Have Android? There is an app developed by DTVThaiVisa.com. If you want to do it alone, I recommend to study all recent questions and answers. Don't be one of the applicants that lose the fees!