visa period and what work do i have to do there?

Dear pradip thapa,

We are pleased to help you get visa on arrival, please apply visa online in this link:http://www.vietnam-evisa.org/apply-visa.html, you don't need to submit us any document. And After 2 working days, we will send you approval letter and give you instruction how to get visa stamp at Vietnam airport.

You just do following our instruction and can get visa stamp at Vietnam airport normally