With the English sounds sh, j and ch, the friction occurs between the alveolar ridge (where the flat part of the mouth located behind the teeth sharply moves up to the palate) and the tip of the tongue. Sometimes, the tongue is a bit further back or curled, and the back part of the tip of the tongue is involved (ie. it is retroflex).
In Japanese, the tip of the tongue is not used for these sounds; instead, a more posterior and wider part of the tongue is used at the point of friction, the tip of the tongue being more or less at the intersection of the bottom teeth and the gum, but without pressing against them.