I am Swedish, but used to come to Helsinki for business monthly for several years.

Start at Salutorget, it is the most famous square with its own herring market. It is a great place to visit if the weather is good.

Then continue to Esplanadi, the commercial street in the centre for Finnish design. Don't miss Marimekko at no 33 https://www.marimekko.com/

There are a large number of great restaurants (for the size of the city). I can warmly recommend Zetor http://www.zetor.net/index.php?id=317 Try the reindeer. it doesn't get more Finnish than that.

Have fun!