While the people of Greece speak the Greek language, English is actually the primary foreign language spoken by more than 48% of the population so you shouldn't have any trouble communicating during your travels if you stick to bigger cities and other tourist locations.
The Greek language is a complex one spanning over 2500 years as an independent branch of the Indo-European language family. While the Greeks are responsible for sharing a lot of modern ideas such as democracy and philosophy, the Greek language isn't closely related to any other world language making it quite unique to Greece itself.
How to say 'hello' in Greek - Γειά σου (Yah-soo)
Easily the word you'll use the most while travelling around Greece and probably one of the few Greek words you've already heard is Γειά σου (hello), pronounced 'Yah-soo'. While this is more formal than the casual Γεια (meaning 'hi' and pronounced 'Yah'), it's still commonly used all around Greece when meeting strangers for the first time.
How to say 'how are you?' in Greek - Tι κανείς (tee-KAH-nis)
If you want to show off your language skills and go one step further than 'hello', learning how to say 'how are you?' is the way to do it. The Greek phrase for 'how are you?' is Tι κανείς (pronounced tee-KAH-nis), and is often used straight after Γειά σου (hello) as a continued greeting.
How to say 'thank you' in Greek - Ευχαριστώ (eff-kha-ri-STOE)
It's always important to be polite wherever you go, especially when you're travelling in a country that's not your own, so expect to say Ευχαριστώ (thank you) - pronounced eff-kha-ri-STOE - a million times a day. As Greeks are friendly, welcoming, and polite people, you can also expect to hear this said back to you a million times as well.
How to say 'goodbye' in Greek - Γειά σου (Yah-soo)
The word for 'goodbye' in Greek is the exact same as the word for 'hello' so once you've learnt it, you'll know how to start and end conversations properly. If you're among a group of people and you want to say a greeting or a farewell to everyone at the same time, simply say the word YAH-sas.
How to say 'please' in Greek - Παρακαλώ (para-kah-LOE)
The words for 'please' and 'you're welcome' in Greek are the same, so you can knock off two birds with one stone by learning how to say Παρακαλώ (please/you're welcome), pronounced para-kah-LOE. This word can also be used as a way to make someone repeat themselves if you haven't heard them properly, as well as when asking for directions or the price of something.
How to say 'yes' in Greek - Ναί (neh)
It's easy to get confused when trying to say 'yes' in Greek as the Greek word looks similar to its English counterpart for 'no'. If you want to say 'yes' to something, use the word Ναί (pronounced neh).
How to say 'no' in Greek - όχι (OH-hee)
The same confusion can be applied to the word 'no' as the Greek word for 'no' is όχι (pronounced OH-hee) but looks similar to the English word for 'okay', thus making you think it means 'yes'. As long as you remember to use these words in the opposite way as you would in English, then you'll be completely fine.