kalimera = good morning. Used both when coming to and going away from a place.
kalinihta = good night. Used only as a goodbye greeting in the evening or at night.
kalispera = good afternoon. Used only when coming to a place or meeting someone in the evening or at night.

yassou = hello or goodbye (greeting to one person or a friend)
yassas = hello or goodbye (greeting to more persons or a more formal and polite way to greet an unknown person)
adio = goodbye

Learn the Greek numbers
ena = 1
dio = 2
tria = 3
tessera = 4
pente = 5
eksi = 6
epta or efta = 7
okto = 8
ennia or ennea = 9
deka or theka = 10
endeka or entheka = 11
dodeka or thotheka = 12
deka-tria = 13
deka-tessera = 14
deka-pente = 15
deka-eksi = 16
deka-epta = 17
deka-okto = 18
deka-ennia = 19
eikossi = 20
eikossi-ena = 21

Common Greek Phrases
Efharisto = Thank you
Parakalo = Your Welcome
Pos se lene? = What is your name?
Apo pou eisai? = Where are you from?
Thelo ena tsai = I want a tea
Thelo mia mpira = I want a beer
Poso kanei? = How much is it?
Ela = Come
Sagapo = I love you
Agapi mou = My love, Darling