Besides having a valid Russian visa in passport, foreign nationals going to Russia are requested to fill in the Migration Card. Migration Cards should be available on a board of airplane/train/ship or on the border control area in case of arrival by bus/car. 

The migration card consists of 2 parts: A (Arrival) and B (Departure). You should fill in both parts and hand it over to the Border Control Officer along with your passport and another travel documents. Part A will be taken out and part B - stamped and returned to you for the following registration procedure.

You should present migration card to make registration of your visa (that must be done within 3 days after your arrival to the point of destination or within 24 hours if you stay in hotel). 

You must keep the original of your migration card as it should be returned to the border control officer while your departure from Russia!