On arrival in the airport, you have to fill in a migration card before going through passport control. Keep this paper with you during al your staying in Russia, because you'll need it:
- visiting other cities in Russia
- deparing from russia you must show your migration card to the custom's officer
Coming to any russian city you should be registered. You can be easily registered it the hotel,you're staying at, or, in the Passport and visas Department of Ministry of Internal Affairs (PVU). You must be registered in 72 hours after your arrival.