All of the measurements go around the circumference of your body.

Bust: fullest part of your bust

Under Bust: ribcage directly below your bust

Waist: smallest part of your waist

High Hip: a long hip bones

Low Hip: widest part of hips a long the glutes

Torso: from the shoulder, down to the crotch
through the crotch and back up to the shoulder

You want to make sure that your measuring tape is parallel to the ground and
that you take your measurement on your relaxed exhale.
For the torso measurement you want to make sure you're standing up straight to
get the most accurate fit. (slouching will change the measurement)