Finland has three official languages: Finnish is the majority language and Swedish is spoken by about 6% of Finns. A minority population in Lapland speaks Lappish. In and around the large cities, especially in Helsinki, you should be able to deal with much of your everyday business in English especially with younger people.
If you have knowledge of the Swedish language, you should note that some words might differ because of the Finnish-Swedish dialect. The Finnish-Swedish accent is also considerably different to the accent of Swedes in Sweden.