Electrical plugs in Finland need two round prongs. They can be the ungrounded Europlug Type C or the grounded Schukoplug Type E/F. So do you need an electric transformer or just a shape adapter for Finnish outlets?
It's not too hard to find out what kind of adapter plug or converter you need for electrical outlets in Finland. Most laptops will automatically work with 220 volts (check the back of your laptop for power input markings.) That means you'll only have to change the shape of your existing power plug to fit into a Finnish outlet.
And that's it. These simple plug adapters are relatively cheap and you can compare adapter prices here.
If you bring small appliances, be careful. The shape adapter may not be enough. While basically, all personal electronics in recent years will accept both voltages, some older, smaller appliances don't work with the stronger 220v in Europe. Check if the label near the appliance's power cord shows 100-240v and 50-60 Hz. If it does not, you will need a "step-down transformer" (also called a converter).
The converter will reduce the 220 volts from the outlet to provide just 110 volts for the appliance. These converters cost a little more than simple adapters. Compare prices of converters here.
Tip: Don't bring any type of hair dryer to Finland. Their power consumption is extremely high and can only rarely be matched with correct power converters that let you use them with Finnish sockets. Instead, simply check if your Finnish hotel has one in the room, or just buy a cheap one after you arrive in Finland.