Dear Kiran Ladva,
Thank you for your question.
To get visa on arrival, you need to fill in the application form online at our website https://www.vietnam-evisa.org/apply-visa.html . After you pay for us, we will send to your email a visa approval letter within 2 working days (for tourist visa). Then you just need to print this letter to board the plane and get visa stamped at Vietnam airport.
Please feel free to contact us if you have any questions.