“sh” [ʃ] –> requires a flow of air through your teeth, which allows you to hold the sound for a long time. (This is probably why the sound is used as a way to say “be quiet” in English).
“sh” [ʃ]
“ch” [tʃ] –> is produced with one strong puff of air through the teeth which is then stopped.
“ch” [tʃ]