The trains between St. Petersburg and Helsinki stop here. Coming from StP you can only get off. This is a crossroad if you want to go into the area near the Russian border. There are also frequent train connections to Helsinki.
There are various buses from here. You can travel all the way to Helsinki which takes longer than by train or to Imatra etc. You can buy the bus tickets in the railway station at a separate counter (where they speak some English) or directly from the drivers (who are not likely to speak English).
In the modern station there are the usual facilities like kiosk, cafe, luggage lockers etc.
Take the train!
Kouvola has one of Finland's biggest "crossroad" train stations, so possibly the easiest way to get there is to travel by train. For example, it takes two hours to travel to Kouvola from Helsinki and a one-way ticket for adults costs around 20 euros, depending on the train.