We don't have the consonant <sh> in Vietnamese but the consonant <s> which sounds pretty much like <sh> in Mandarin. For example:
sử (history) sounds close to 十 shí
san (mountain) sounds close to 山 shān (Surprised? A Chinese-Vietnamese word)
sân (house/school yard) sounds close to 身 shēn
Depends on the dialect. In the north (if memory serves) s is pronounced like a retroflex s, like Russian ш or Polish sz, or Hindi ष, transliterated as ṣ (as in the name Kriṣna).