The names of the letters?
Normally that depends where you live, the English pronounce them as if they were English words and Germans as if they were German and so on. the biggest difference is the i.
Xi is like ksi, tau as in tower only with out the last two letters
, chi as in shi and phi and psi as they are written, you can choose how to pronounce the i really. Here it is pronounced like ee but i think in england it's like I (personally I think ee is better). Hope that's any help.