Visa on arrival is an alternative way to obtain a visa for Vietnam in addition to the traditional way of getting a visa at Vietnam Embassy.
With this kind of visa, you – the visa applicant is required to submit an online application for a visa approval letter which functions as an official permission allowing you to board the flight and have visa stamped at the arrival airport in Vietnam. To get visa stamped, you need to submit your Vietnam approval letter together with your passport (at least 6 months validity), one passport-sized photo, entry and exit form and stamping fee to Immigration Officers at the airport.
There is a basic difference between visa on arrival and visa at Vietnam embassies. With visa on arrival, the Vietnam Immigration Department will issue a visa approval letter with your name on it stating that you are allowed to enter Vietnam on a specified date. Then, you will have the visa stamped onto your passport at the arrival airport in Vietnam. But for visa applied at the Vietnam embassies, the visa stamp will be on your passport when they send it back to you.