You can easily reach Helsinki Airport by train from all around Finland. Commuter trains (company HSL) P and I goes to the airport frequently from Helsinki city centre, Pasila and Tikkurila. 

Helsinki Airport train station is located right next to the terminal. From the train station you'll get to the terminal by an elevator or escalators. 

You can search for routes and timetables from the operators' own websites:

- Commuter trains: HSL website

- Long-haul trains: VR website