I won't explain mounding here, except to say that essentially, you put soil in the pot, put one plant in with the root ball basically on top of the soil. In mine, at left, I started with the tall echeveria decora in the middle (probably too tall for this composition, but whatever). Then you kinda wedge the root balls of the other plants around the first one. It feels weird to plant plants at an angle, but it works (and is much harder than you might suspect!). Fill in the spaces with soil, then when you're done, cover the exposed soil with pebbles, and voila!
I'm sure we both have a lot to learn about the technique of mounding, but we had a blast trying it for the first time!