I'm a little confused on how we are supposed to describe the transformation for a horizontal stretch.

ex. -1/2 f(1/3x+2)-6

- vertical compression by a factor of 1/2
- horizontal stretch by a factor of 3 (is this how you would write it? Also is
horizontal stretch even the right or is it horizontal compression)

the graph of y = f(ax) scales the graph hoprizontally by a factor of 1/a

For example if y=x^2
then y = (2x)^2 scales the graph by a factor of 1/2

See
https://www.wolframalpha.com/input/?i=plot+y%3Dx%5E2%2C+y%3D%282x%29%5E2