Piraeus,a city in the periphery of Attica and a suburb located around 9 km to the south-west of the center of Athens actually lies at the western part of the Athens coastal zone.
As it belongs to the Athens urban area, it was the port of the ancient city of Athens and was chosen to serve as the modern port when the city re-emerged.
In view of this backdrop, here is an attempt to give certain guidelines if you happen to be at the tourist location Piraeus for the first time as the problem of language is bound to be there and most of the information available in the city or either over internet is gloomily not in English.
Monastiraki metro stop:
If your journey begins in the city of Athens rather than at the airport, the cheapest way to get to Piraeus is by the simple & easily available metro. Monastiraki metro stop is the best option where you don't have to change trains if you just start your journey at Monastiraki in the first place.
Other stations direct to Piraeus are: Tission & Omonia. You can also take the Syntagma station which is the new & beautiful metro spot with a transfer in Monastiraki that will drop you right in front of the Piraeus Centeal Port.
Filippis Tour agency:
Piraeus is blessed with one of the most kind Travel Agency called Filippis. Known for its hospitality and best of services, the agency offers reasonable costs with kind and soft-spoken workers who speak Greek, English and Italian which is indeed a boon when you land up for the first time in a European city like Piraeus.
Express bus, Trolleys:
One can also avail the mode of express bus facility & trolleys from Athens international airport where a very good network from E96 connects the airport with the port of Peiraias, metro line 1.
Bus and trolley tickets can be purchased at special booths and kiosks near the bus stops. The tickets prices are sensibly charged.
You can validate your ticket by asserting it into one of the meters that will get punched and dated.
Be cautious & keep the ticket until you leave the bus, since it's not uncommon to have a ticket-checker to check their validity. If you are found that you haven't punched your tickets, then chances of penalty/fine can't be avoided that might require you to pay a few Euros. So, better prevent the embarrassment by following the correct procedures.
Do NOT validate your 24-hour ticket more than once.