If you hold Myanmar (Burma) passport and want to visit Vietnam for less than 15 days, you do not need to go to Vietnam embassy asking for visas. For more than 15 days, you also do not need to go to the embassy neither; you can just apply for Vietnam visa online here, on this website.
Applying online is simple, fast and cost-less, it just takes you a few minutes to fill in the application form then you can relax and wait for the approval letter from Vietnam Immigration Department. When your application has approved you just bring that letter with you to a Vietnam international airport and have your visa stamp here.
Here is the embassy address if you still need to.
Vietnam embassy in Myanmar