If you stay in Belarus for five (5) or more business days excluding weekends and Belarus public holidays then you will need to register your visa. If you are transiting through Belarus or staying less than five (5) working days then you do not need to register your visa, though you will still need to ensure you obtain a migration card as described below.
When you cross the border into Belarus, for example overland by train from Poland or by air from London into Minsk, then you will be given a migration card which you will need to complete. The card is in two parts, part "A" and "B" and both parts need to be completed (in block capitals) before you go through passport control. Part "A" of the card will be kept by passport control on entry and part "B" is returned to you with an entry stamp on it - do not lose this card, keep it with your passport at all times.
Mandatory government insurance is sold at Minsk international airport upon your arrival and this is required for your registration. If you travel to Belarus overland, for example by train or car, it is your responsibility to obtain the insurance in the city where you are staying before you go to get your visa registered. The two Belarus companies that offer insurance to foreign visitors are Belgosstrah (БЕЛГОССТРАХ) and Beleximgarant (БЕЛЭКСИМГАРАНТ), both of which are owned by the state.
If you are staying at a hotel, the hotel will register your visa for the duration of your stay at the hotel during the check-in process by placing the hotel registration stamp on part "B" of the migration card.
If you are staying at a private apartment or house then you need to be registered at the Passport and Visa Department in the town, city or district where you are staying. Your landlord or host will need to go with you and you will need to present your passport, part "B" of your migration card, proof of insurance and pay the registration fee of £4.00 (in Belarusian Roubles). The Passport and Visa Department registration stamp will go on part "B" of the migration card.
When you leave Belarus you need to present passport control with part "B" of your migration card containing your entry stamp, and, if required your registration stamp(s) from the hotel or OVIR.
If you have failed to register your visa correctly or lost your migration card, then you may have problems with passport control when leaving Belarus including fines of several hundred US dollars.