You True South is your Longitude position, negative longitude readings = West, positive East, e.g., -1.234 = 1.234 West.
If using USALS, you don't need to align the dish, to true South, you set everything up to 0, enter your Latitude, and Longitude, into your receiver, and use your receiver to sent the dish to a suitable satellite, like 0.8W.
Then you physically move the dish, and motor, on the mount, to get the strongest possible signal, on 0.8W, also adjusting the elevation, to get the strongest signal.
You then send it to your furthest East, and West, satellites, to check the signal quality, moving it back to 0.8W to make any minor adjustments.