For people who need visas for Japan, the office for international academic support, Hokkaido University, will prepare an invitation letter for you. Please send your travel itinerary to email@example.com.
Transportation to Sapporo
Most of participants outside Japan may fly from Tokyo Haneda (HND) or Tokyo Narita (NRT). There are many flights from Haneda (HND) to New Chitose (CTS) airport (a few flights per hour on average). The flight time is about one hour, 40 minutes.
The following page may be useful when you fly from Tokyo: https://www.japan-guide.com/e/e5306.html
From the CTS airport to the JR Sapporo station, take a rapid airport train. All the trains from CTS are "rapid airport train" getting to Sapporo. So you just get on the available one. Trains leave the airport every 15 minutes. It costs 1070 JPY. If you pay 520 JPY more, you can have a reserved seat. It takes ~40 minutes to the Sapporo station. Please do not get off at the Shin-Sapporo station.