the Russian "sh" - Ш, is represented in Polish by "sz".
To reproduce in English the Russian "sh" character Ш, which is represented in Polish by the letter combination "sz".
The trouble with Polish orthography is that when the missionaries from Rome arrived at the court of King Mieszko they were much less inventive with the Latin alphabet than the emissaries from Byzantium were with the Greek one when they turned up about the same time in Kiev-Russia.
The fearsome appearance of printed Polish stems in a large measure from things like having to use four characters to reproduce the Slavic "shch" sound, whereas Russian uses only one.
Actually Polish is entirely phonetic and dead easy to pronounce once you know what sounds the letter combinations represent.