Greek Dipthongs

A dipthong is two vowels that form a single sound together.

αι ai as in aisle
ει ei as in sleigh
οι oi as in foil
υι uee as in queen
αυ ow as in how
ου oo as in mood
ευ e as in obey + u as in dude
ηυ e as in met + u as in dude

In some Greek fonts, "υ" and "ν" are difficult to distinguish, but in the font used in this site, Palatino Linotype, they are easily distinguished, once you become used to them.