1. You will need to take your invitation letter with you when entering the country. You will also have to fill up a form on arrival in the country. There are various different templates available so make sure to select the one for foreigners from the United States. Don't leave out any details in these forms. You will also need two photographs of yourself along with your passport. Once you have collected all these documents, all you have to do is pay the fees and you're done.
2. The information provided in the form will include a lot of things including your full name, your date of birth, place of birth, current citizenship, passport number, date of arrival and departure from the country, etc. If you have visited Vietnam in the past, you will have to enter information about your visit as well.
3. There are certain countries whose citizens are allowed to enter Vietnam without getting a Visa for a certain period of time. You should find out if you belong to any of these countries as that will mean you don't need to get a visa at all. Citizens of countries Singapore, Indonesia, Thailand, Malaysia, Cambodia and Laos don't need to get visas as long as they don't plan on staying longer than thirty days. If you reside in the Philippines you won't need to get a visa as long as you leave within twenty one days of arrival. In case you stay in countries like Norway, Sweden, Finland, Japan, South Korea or Russia, you can visit Vietnam without a visa as long as you leave within fifteen days. Remember though that you will need to provide confirmed departure tickets to prove that you will be leaving the country within the stipulated time before being allowed to enter.
Getting a vietnam visa isn't as difficult as most people believe although you will find yourself in considerable trouble if you don't have your documents in order. I would recommend hiring a local travel agent to help you with the formalities. It won't cost you more than $ 10 or $ 15 and all your work will get done in much lesser time than if you tried to do it on your own.