Athens Metro Map
Unfortunately this map won't fit on your screen but if I reduce it then you won't be able to read it so just make the best of it and when you get to Athens you can get one from the EOT office.
Athens Metro Information
Right now the lines working are the green line from Pireaus to Kifissia, the red line from Ag Dimitrios to Syntagma to Sepolia, and the blue line from Monastiraki to the airport. Tickets are .75 Euros. Trains run from 5am to midnight. The trains from the airport cost more. 8 euros per person.