Adjective: regular, common, ordinary, usual, normal.
Many meanings, so see the sanakirja.org entry for more.
Let’s translate the whole movie title, ”Se tavallinen tarina,” or ”The Usual Story.”
Se is a pronoun that means ”it” or ”that”, however it is sometimes used as a definite article in colloquial Finnish due to the influence of Germanic languages and English. Its usage here is simply ”the.” It is unnecessary in proper written Finnish where the difference between ”a” and ”the” can be determined by word order. See this link for more on that.
Tarina is a noun that means ”story” or ”tale.”