The Anchor Tool is found at the top of a shape layer's properties panel, which appears in the Inspector on the right side of the interface when a shape layer is selected.
The anchor tool can be used to move a layer's anchor point. An anchor point is the point from which all transformations (changes in position, rotation, shear, and scale) of the selected layer derive from. You can think of it like the pivot point of the shape layer.
You can change the anchor point in two ways:
By clicking any of the dots in the 3x3 grid displayed on the anchor tool
By clicking the eye on the anchor tool (to display the anchor point on the canvas) and moving the newly-displayed, blue crosshairs icon anywhere on the canvas