Use this tool to create new vertices, or select existing vertices.
You can temporarily select this tool by holding the "a" key.
Connect
Use this tool to create a new vertex connected to any previously selected vertices; or click on an existing vertex to connect it to previously selected vertices.
Split
Click on an existing vertex, and any edges between previosly selected vertices and the clicked one will be split in half by the creation of a new vertex at the midpoint of each edge.
Disconnect
Click on an existing vertex, and any edges between previously selected vertices and the clicked one will be removed.
Select
Use this tool to select points by clicking them, or by dragging a box around them. (Note that hidden points cannot be selected this way.)
You can temporarily select this tool by holding the "m" key.
Center
Clicking anywhere in the document with this tool centers that point in the field of view.
You can also zoom in or out while centering by holding the command or option key, respectively.
Add Bone
Use this tool to add a bone, or select an existing bone.