This video walks through a number of things:
1. Slope units
2. How to evaluate raster values
3. Zonal Statistics (summary statistics)

Timestamps:
00:00 Introduction: what we have to work with
00:37 Running slope in % rise and why
02:05 Using raster values (contents pane) to understand the meaning of your layers
02:50 What does slope in percent mean?
04:15 Hillshade values
04:51 Evaluating elevation raster values
05:15 Evaluating unknown rasters
06:11 Differentiating slope in degrees and percent
06:40 How do you know if you are using Zonal Statistics correctly?
07:20 Use Min and Max values from zonal statistics to confirm you are summarizing the right raster surface!
08:17 The Mean is NOT the average of the min and max value!
09:00 Predicting mean in percent relative to mean in degrees... higher or lower?