Surnames for families and clans are very old in eastern Finland while in western Finland, like in the other Nordic countries, surnames were not used until quite recently.
Surnames in Finland often derive from farm names or from given names. The ending -la/-lä turns a word or a given name into a farm name. The same ending is used in western Finland for surnames, while in eastern Finland the ending for surnames will usually be -nen.
In the middle of the 19th centuries also people who had not taken a surname by then began to take Finnish surnames.
In the 16th and 17th century sometimes patronymic forms were used like in Denmark/Norway/Sweden and in Russia.
To create an Finnish primary patronym, the suffix -poika (= 'son') or -tytär (= 'daughter') is added to the genitive form of the father's name. You will find the genitive forms of Finnish names in the grammar tables on the respective name pages.