I bought my MacBook Air in Finland and it has a Scandinavian keyboard. Many symbols appear differently on screen from those showing on the keys. Is there a way to fix this?

Presumably it had Finnish set as the operating language. If you change the language that is what happens!

You need to go to system prefs/keyboard/input sources and make sure the item chosen there is correct for your hardware keyboard. You can see the choices at

How to identify keyboard localizations - Apple Support

Swedish Pro is a likely match