Practical guide for the participants of the first Gemini Autumn School on Quantum Computation
You can find the current travel restrictions to Norway here. Oslo Gardermoen Airport (IATA: OSL) is the main airport for Oslo. This entry in Wikitravel gives a good overview of the connections to the city from the airport. Another option is Sandefjord Airport (IATA: TRF), but it has fewer connections to the city.
The public transportation in Oslo is operated by Ruter and includes T-bane (subway), bus, tram, commuter train, and non-sightseeing boat lines. Ruter has its own mobile app Ruter, which can be used to buy tickets valid from 60 minutes to 1 year. Other than traveling from and to the airport, Zone 1 should be enough to get around.
Alternatively, one can use Reisekort (Travelcard).
Norway has its own currency, Norwegian Krone. However, practically every business accepts credit cards, so usually you do not have to carry large amounts of cash, if any at all. ATMs are called minibank.