Answer
Please note that Russian passport holders are not required visa for Vietnam if you stay less than 15days. (According to the decision from Vietnam government, citizens of Russian, Danish, Norwegian, Sweden, Finnish, S Korean, Japanese are not required visa for Vietnam if stay less than 15days, citizens of South East Asia countries, except Myanmar are not required visa for Vietnam from 15days to 30days)
For Russian passport holders, you should apply for a visa to enter Vietnam if you stay more than 15 days, of course you can enter Vietnam with visa free policy then extend your stay but it is better to apply visa if you stay more than 15 days.
For apply visa on arrival Vietnam at the airports, you fist must have the approval letter from Vietnam Immigration Department, show that letter for boarding and show on arrival at land visa office to get visa stamped on your passport.
To get approval letter from Vietnam Immigration Department for picking your visa on arrival, you can request through an agent in Vietnam or apply online with us. Within 1 - 2 days after you paid an small amount for service fee they will send approval letter from Vietnam Immigration Department to your email. All you have to do is print the approval letter with instructions from the visa agents and bring them to get visa on arrival at Vietnam airports.