Greece is a popular vacation destination. That's why many network providers offer english version of their websites and tourists buying Prepaid SIM cards is nothing unusual
There are 3 network operators in Greece: Cosmote, Vodafone and Wind. They use European standard frequency bands. Best coverage is provided by Cosmote.
You always have to verify your identity with e.g. a passport to get a SIM card.
Be aware, that local dealers may try to sell you unnecessary upgrades.