Citizens of a Nordic country must usually submit a notification to the local register office if they stay in Finland for more than 6 months. The Nordic countries are Sweden, Denmark, Norway and Iceland.
The person moving to Finland must personally visit the local register office and fill in the Registration Form for Foreign Nationals. The register office stores the information in the Population Information System and issues the person with a personal identity number.
The same procedure applies to Nordic citizens moving to Finland from countries other than the Nordic countries.
Registration of foreigners (maistraatti.fi)