Driving is fairly easy in Finland. You can refer to the driving rules Brochure for the rules. 

However, do remember that google maps is quite good. 

You do not need to waste money on renting a GPS from the Rental agency. A top up of only one euro per day on a prepaid phone SIM takes care of all the directions you need, as opposed to Euros 12+ per day  for  GPS from any rental agency.