Buses are an easy and inexpensive way to travel round Lisbon. There’s also no better way to make yourself feel like a local. There are about 78 day buses serving the 5 zones of the city:
Pink: Ajuda and Belém Blue: Benfica and Carnide Green: Lumiar and Alvalade Red: Marvila and Olivais Orange: Central Lisbon
And don’t worry; if you go out clubbing, there are also 9 night bus lines to take you home in the early hours.
A single bus journey is € 1.50 if you pay when you board. But it can be a bit cheaper with a 7 Colinas (internal link) card.
And, if you happen to get on the 36 or the 745, make sure you have your laptop because there’s free WiFi access. You can then use it to look up your bus on this route finder.