front you turn your body/shoulders forward down the slop.
backside you you turn back up the hill. this is also called "blind" since when you turn your shoulders up hill you loose sight of the end of the rail/ landing.
if you dont understand that picture this...
your sliding a rail right foot foreward. if you spin to the right you turn your body downhill aka frontside swtich up or fa front side spin off
slide right foot foreward again but spinning to the left out, your body turns up hill and you loose sight of the rest of the rail and land for an instance aka back side or blind switch up or spin out