Your friend is mostly correct, but in these sounds, he is a bit off.Originally Posted by PsiLord
"c'" sounds very much like Russian "ч"
"cz" has no exact match in Russian; there is a similar sounds in Bielorussian, though - this is "hard" (not palatalized) "ч" (For those who heard Lukashenko speaking on TV, imagine him pronouncing "чай").
s' is softened "ш" - it sounds very much like a short "щ"
z' is a voiced ("звонкий") counterpart of "s'"
I can't insert Polish characters here, so I used c' instead of c with an "accent mark" above etc.