In order to apply for a Belarus private visa, you need to have the original of an invitation, issued by the local Citizenship and Migration Department (OGIM) in Belarus.
This procedure has been simplified for the citizens of migration-secure countries. For example, a UK or a USA citizen can put the personal details of the person from Belarus in the visa application and mail it to the local consulate of Belarus with the passport, passport-size photo and a consulate fee receipt. This private visa is valid for up to 30 days.
Keep in mind that if you choose a simplified visa application the consulate still may ask for the invitation original. This will consume some time and effort from the side of your friend from Belarus.
If the consulate of Belarus requires the original of an invitation letter from your Belarusian friend, he or she will have to take the following steps: pay the state service fee, fill in an application form for a private invitation letter at the local Citizenship and Migration Department (OGIM) and collect the paper 10 days later, and then mail the paper to your country or MSQ Airport Consulate.