You can add, move and edit Knee and Spline Points by using the mouse and the keyboard modifiers:

• Left Mouse Button: Insert Spline Point
• Left Mouse Button + Shift Key: Insert Knee Point
• Drag Point out of Window: Delete
• Drag First or Last Point + Ctrl Key: Set same Y value
• Drag Point + Ctrl Key: Set only Y value
• Drag Point + Alt Key: Match X,Y to Grid
• Right Mouse Button: Zoom -> Scroll -> Normal Mode
• DblClick: Reset ViewMouse Wheel: Zoom 

The button row allows you to modify or generate the curve:

• Symetric: The curve will be symmetric  on X/Y axis. No unsymmetrical editing is allowed
• Reset: The curve is cleared to the defaultSteps: Enter the amount of creation steps
• Create: Choose different spline generators
• Mirror: Mirror the curve at the Y axis
• Invert: Invert the curve at the X axisLoad: Load a spline definition from a *.spi file
• Save: Store the current spline in a *.spi file 

Note: The spline editing is fully integrated into the crushers undo/redo system

Sometimes a modulator fader is visible. That allows the “modulate” the current spline curve. This blue curve is used as the resulting spline.

Note: You can control also the spline modulation fader by MIDI/Joystick/VSTParam. Use the learn functionality on the fader.