Ternary plots (aka Triangle plots) have three axes rotated and layered on top of each other. So when you get a point like this:
You read it as 50% of the way up the clay direction:
30% of the way up the sand direction:
20% of the way up the silt direction:
So it is 50% clay, 30% sand, and 20% silt.
From a recent vacation: