So if your car includes a turbo then the HUD includes a boost gauge. What information exactly is this boost gauge conveying to me and how can I use it to be a better driver?
You literally cannot use it to your advantage in any way. Once the throttle is fully pressed, the needle will go as high as it will (the max pressure the turbo in said car operates at), and sometimes the figures on the gauge are misleading as well.
It's merely there to tell you this car is turbocharged.