Probably the easiest way to reach the venue of the conference (Hotel Forrás, Szeged) from Liszt Ferenc Airport, Budapest, is to take a shuttle service from the airport to the venue.
The following shuttle companies proved to be reliable and prepared for foreign passengers in the past:
https://zoldtranszfer.hu/eng.html
http://pegazustranszfer.hu/en_EN/online-megrendeles
Although more complicated, it is also possible to use public transportation. From Liszt Ferenc Airport you can take the bus 200E (tickets can be purchased at the airport from ticket machines) to "Ferihegy" or "Kőbánya-Kispest", get on a train (tickets can be bought online at https://www.mavcsoport.hu/en ) to Szeged trainstation, and take a local bus or tram there to the venue. Google Maps can help you with planning this part of your trip.