For every object on the slide you can set a "Follow Path" start/end/anim effect. You will notice this effect will display an Edit button instead of the usual "..." button.
Pushing this button will switch the main area in edit mode. In this mode you can:
- Add new control points: by left clicking on the slide.
- Remove control points: by right clicking on the slide.
- Moving control points: by dragging control points.
- Changing settings: If you right click anywhere on the slide, a contextual menu will appear. You can change various settings of the effect using this menu.