Each axis runs 0 to 100 clockwise. At any point in the triangle you represent a location 0 to 100 for any given axis. Remember that the axis are rotated relative to each other by 66 degrees, not the normal 90.

Edit: For example the top vertex represents 100 on the clay line but 0 for loam and silt. Whereas the top left corner of clay loam represents values of 40 clay, 45 sand and 15 silt