The Direct Selection Tool selects
and moves existing path's / vector shape mask's segments / anchor points:
In the Toolbox, select the Direct Selection
Tool.
Drag on the image to select a path or shape segment
or click directly on an anchor point to select it*.
Drag selected anchor point or segment (by an
anchor point) to re-shape path or vector shape mask.
Drag direction point of a selected anchor point
to change curve's amplitude and / or direction.
To delete selected segment or anchor point press [Delete]
key.
To select 2 or more segments or anchor points
press [Shift] key while selecting.
*In case the work path / vector shape layer is not currently selected, first click on a path or shape to select path / layer name, and then select its segment or anchor point.