The title pretty much says everything, How do I curve a motion path?
Just create a new keyframe (pressing I key), with the motion tool selected if you only move the curve, or transform, rotate, skew or scale tool if you want modify in point these properties in the selected element.
Create this keyframe in any point of the peg, different to the first keyframe or the last. Then move it in camera window, dragging the element with the motion tool, with the timeline cursor in the same place that the new keyframe. This create a locked in time point, named Motion Point. This point don´t modify the number of frames before and after it´s position. You can modify the Tension, Continuity and Bias properties to make more smooth or more hard the curve. Keep selected the created point in camera window to access the keyframe properties panel.
You can also create a Control Point, (green diamond), unchecking lock in time button in the properties panel for convert the created motion point, or shift-click in any other point of the peg, to create other control point in the peg trajectory. This point is not locked in time, and You can move it into the frames as floating point. You can convert this control point in motion point by checking the lock in time button in the properties panel.
I hope that be helpful. Best Regards. Yoryo.
I need clarify You that when create motion curves, you must hook the visual element into a specific element called PEG, that make possible the path visualization and keyframe control. For manipulate motion keyframes You must use the Motion tool as specific tool. You can also hook the camera to a peg element to make a motion camera trajectory. You can read explanation about PEGS in page 400 and next in ToonBoom 5.0/Help/User Guide. Yoryo.