Dual rates and expo settings are largely personal preference of the pilot. I can provide you with my recommendations, and how I typically setup my planes.
Expo (exponential):
This setting alters how sensitive the sticks are around the center point. It does not alter the total throw of the servo movement. It alters the default linear curve to one that either is less sensitive (positive expo) or more sensitive (negative expo) around the middle point. Typically, I start with 30% for all my aircraft on all surfaces, and then alter as deemed necessary. This allows for a little more stick movement around the middle for more precise flying. Typically 25-40% expo on control surfaces is typical for beginners.
Dual (multi) rates:
Dual, or multiple, rates controls the total deflection of the control surface. On most of my models I setup 3 rates. This is mostly due to using a Taranis radio where most all the switches are 3 position. It allows me to setup a low, medium, and high throws on any or all of the control surfaces. For the Flite Test models, where typically only low and high deflections are published, I setup my multiple rates like this: Low rates match the Low throws specified in the build, Mid rates match the high throws specified, and high rates utilize the maximum servo throws allowed without binding the servos. Think of it as low, high, and crazy.
By mixing your preferred expo and rate settings in the radio, you can instantly switch from precise control with lower throws to full aerobatics with high/extreme throws. The expo setting will assist in the sensitivity around mid-stick.
I hope that helps! I suggest that you start off with some safe recommendations, and then experiment to your liking as your experience grows. Good luck!
