Process Designer comes with several pre-designed system models in the Tools pane, such as Select Background Points in the Classify Points for Cartography group. These models have a special icon:
. You can add a system model by double-clicking on it or dragging and dropping it.
The *.processmodel files for these models are stored in the program directory under /system/Process Designer/Models/. These files cannot be edited, but you can copy them and customize them as you see fit.