
The fill colour of the selected object. There are colour chips for each colour supported by the current colour mode, plus “Erase” and “None”.
The colours available:
Note that Hierarchical and Palette actually share a colour value (i.e. you can’t have Primary on one and Secondary on the other!). This is an Apple restriction.
When changing your colour to or from Erase or None, this applies across all colour modes. If you want to separately configure your object’s colour per mode, use the divergence button to the right of the colour chips:

The width of the stroke, in points.
Stroke width is the most common way of producing the different symbol weights. As such, the default stroke widths are shown here:

Unless you’ve unlinked the geometry for your selected object, then changing the stroke width in the inspector will change it for all weights, keeping the same ratio. You can edit it per weight using the divergence button to show the popover, or by unlinking the geometry for your object using the floating button on the canvas.
Stroke colours follow the same logic as fill colours. Again, if you don’t want your object to have a stroke, choose None for the stroke colour.
The style for line corners: Round, Miter, or Bevel.
Note that Corner: Round is describing how to draw the lines that form the stroke. It’s not the same as your shape itself having rounded corners (which can be found on the Size/Metrics inspector).
The style for line ends: Round, Square, or Butt.