The city of Athens has a very comfortable transport system, and it’s really easy to move around even if you are travelling without your own car. Athenstransport.com is the official website of all means of athenian transport and the place you will find all the news and updates of every day.
From Athens Airport El. Venizelos: To get in the city from the airport, there two ways. Either you will take the blue line (M2) of Athens metro and take off to Syntragma, the central Square of Athens or the bus X95 that also end up its route to Syntagma.
From Piraeus port: If you arrive in Athens by ferry, then use the green line of Athens metro (M1) and get off either in Monastiraki or Omonoia which are two central spots of the city.
From Central Railway Station (Larissis Station): If you travelling by train, then use the red line (m3) of Athens metro and take off to Acropolis or Panepistimio to get in the city center.
An easy way to use all means of transport to arrive at your destination easy and comfortable without feeling lost, apart from using Google Map App, is to use also the app OASA Telematics, especially if you uses buses often, so that you will know the exact time the bus arrives or your stop you want to take off.