Helsinki is a great city to cycle in as it is very flat and there are well maintained and clearly marked cycle paths.
You can plan your route and have the cycle paths mapped out for you at: Reittiopas
Bikes can be taken on the Metro and commuter trains, provided there is space. Bikes are not allowed on the commuter train during peak travel times. Bikes on Public Transport
The City of Helsinki has a cycle service centre at Narinkka Square (Narinkatori) in Kamppi. The Bicycle Centre ( Pyöräkeskus ) offers emergency repairs, bike parking and a free pumping station. Visit the Bicycle Centre for more details.