The goal of Finnish Bowling (Mölkky) is to score 50 points.
If you hit one pin, you get the score that's on the pin. It can't be touching any other pin to get the points on it.
If you hit more than one pin, than you get the number of pins that are knocked down.
You have to hit exactly 50 points. If you go over 50 your score automatically goes to 25.
You must throw underhand. Throw 3-4 meters away from the pin formation. After each throw, the pins are put upright exactly where they were knocked down to.
A player that misses all the target pins 3 times in a row is eliminated.
Here is a link to the detailed rules. Rules also ship with the game.
Here is a link to the app to help you keep track of the score.