I applied for my wife for tourist visa one year back. I just followed the process on that link I sent you. You have to complete the online application form. All they require is in there. U don't have to fill it all in one go. You can save it and continue later also. Attach a file with your photo with the application. You have to choose a suitable interview date (could be upto a month later). Print the form which has a reference no. Take that to commercial bank (i think) to pay the fees. At the interview you have to prove that you are doing well in Qatar and that you will return back. If you can, get an invitation letter made from any friend/ relative in US and take it with you.

It is very straight forward - just follow the instructions on the website. It is really there to guide you.