Citizens of few countries are required to have a visa for entry into Finland. Check the requirements here.
Helsinki-Vantaa airport is located about 25 km north of the city centre.
Bus no. 615 : Single fare from the airport is 3.60 EUR, and the journey time is about 35 minutes to the main railway station. From the railway station it is about about 0.5 km to the University or the hotels. The bus ticket is valid for transfers within 80 minutes, so you can continue by tram to the university/hotels if you prefer not to walk. See the Journey Planner for the exact route.
Finnair bus : Single fare is 5.20 EUR, journey time is 35 minutes and the bus goes to the main Railway station like bus no. 615. But note that the ticket is not valid on any other means (trams, other buses, etc.).
Airport taxi : The airport taxis (yellow minivans) have a flat rate of 22 EUR and leave when the minivan has enough passengers. (1-2 persons is 22 EUR, 3-4 persons 28 EUR).
A "normal" taxi (yellow taxi sign on the roof) to the centre of the city/university from the airport should be about 35 EUR. All taxis have a meter and charge the same rate, and they accept major credit cards.
Helsinki City Transport
Helsinki City Transport will take you around in Helsinki. (But note that the conference venues are within walking distance from most of the hotels.) A single fare ticket on the trams is 2.00 euros and valid for one hour. A single fare on any means (bus, tram, metro, ferry) is 2.20 euros and likewise valid for one hour. You buy the ticket from the bus or tram driver, or beforehand from a kiosk or a ticket machine.
Use the Journey Planner to find your way with the city transport.