To reach Helsinki city center from the airport, these are the easiest options:
Helsinki city center, where the university and conference are located, is fairly dense and walkable. However, the city is well-connected by a public transit network of busses, trams, metro (subway) and local trains.
The operator of Helsinki's public transportation network is HSL, and buying a HSL ticket entitles you to use any and all methods of public transport within the city. Individual tickets can be bought from ticket machines, bus drivers or using a mobile app (requires a data connection). Individual tickets are also sold in R-kioski (a small convenience store). Note that tickets are not sold on commuter trains but must be bought in advance. If you are planning to use public transportation more often, the most price-effective option is to get a ticket for a pre-set number of days (1-7 days).
If you need to know which route and method of transport to take, visit HSL's Journey Planner. Just write your departure and arrival address, and it will offer you the fastest route as well as a map where the route has been marked.
Hotels
There is a wide range of accommodation options in Helsinki. However, Helsinki is a popular tourist destination in summer so please be sure to book your room well in advance.
This list of hotel options is certainly not exhaustive. You can find a more complete listing here.