Construction lines
The shape creator works by defining construction lines that will let the tool know where are the major facial features of your mesh.
In your Scene view, make sure you have Gizmos shown, and move your Scene view to focus on the face of your avatar.

Facial structures
The examples in this document will show three avatars (Karin, Foshunia, and Actias) as supporting examples.
These three avatars have different facial structures. Use them as references for your own construction lines.