As soon as you enter this mode (as with all modes) it will show you a description on-screen of what special operations are available in that mode:
If you forget what the mouse can do, keep your eye on the bottom right corner of the window and see how it changes when you hold down Shift or Ctrl (or both). When in faceting mode and holding down Shift, it looks like this:
That tells you what the mouse can do.
OK, so let's make a truncated pyramid, also known as a podium. Well, actually Ulrich might have had it slightly wrong. He was making an anti-podium, so let's do that (lateral faces are triangles rather than quads).
First, the resulting solid will not have dihedral symmetry, so from the drop-down list that initially says "8-fold Dihedral" select "8-fold Pyramidal".
Let's start with the big base octagon. Just hold down Shift and Left-click on each vertex in turn around the base (actually after doing three you can hit the "..." button to auto-finish the polygon).
Then hit Enter to accept this polygon as complete.
Do same again for the top octagon, using vertices closer to the centre.
Now create the lateral triangles. Here's one being created, but not accepted yet:
And here it is after accepting (it's repeated over the symmetry group, so 8 triangles are created).
There are still green edges. These represent edges that are not complete yet, that is, they only have one face so far (a face still needs to connect to another face at these edges). So create the final type of lateral triangle face to get this:
No more green edges, so all seems well. Create this faceted polyhedron by clicking on the left-and-down arrow button in the titlebar of the faceting preview window
If you really did want a podium rather than an anti-podium, then you would start with an octagonal prism instead of antiprism, and create lateral quads.
Alternative method
As Ulrich mentioned, there's also an easier way to create these, but you don't currently have precise control over sizes (must judge by eye instead). This is to use augmentation mode, which can create anti-podiums directly. Start with an antiprism as before, but don't subdivide the faces. Again, drop to 8-fold pyramidal symmetry. Select the top face (you'll want to leave faceting mode first) and hit "a" for augment (or use "Poly->Augment Polyhedron"). Lots of options come up, but you can ignore most of them. Select Antiprism from the choices at the top and hit enter. You should see something like this:
Hold down Ctrl and notice the mouse tips in the bottom right corner of the window:
So while holding down Ctrl, hold down the right mouse button and drag the mouse left and right. You will see the width of the top of the antiprism get bigger or smaller. Also try the left mouse button and drag to change the height. Hit Enter when you're happy and with to keep the result.
You can then select the new top face and repeat the process to add more layers. Should be quite fast and easy, and the augmentation options box will remember your settings from last time, so you don't even need to keep selecting the Antiprism option.
Hope that helps.
Rob.
