A 7-day card to the Stockholm public transportation system (SL) is provided as part of the main conference registration package. It is valid from Friday 13/7 through Thursday 19/7 on all public transportation operated by SL. This includes most buses, subways and commuter trains. The most important exception is the Arlanda Express fast train from the airport to Stockholm central station, which is not included.
You get the metro card when you pick up your badge at the registration desk.
The SL web page has a travel planner that can help your find the route to your destination.