Lisbon is a nice city to walk and it is well served by a public transportation network that includes subway, busses and tramway. If you want to visit the outskirts, you can catch a train or a boat, depending on where you want to go. Taxis are cheap and there are other companies such as Uber and Cabify. Bike sharing is growing, and you can rent a bike via Gira or Uber.
For information on how to go to the conferenece venue, please check the venue page in this website.