A sketch is a collection of 2D edges. A plane can hold any number of sketches. Whenever you create a 2D edge using one of the tools in the Draw Toolbox, it is added to the currently "active" sketch. You can click the New Sketch button to create a new sketch in the currently "active" plane, or you can select an already existing sketch to make it the new active sketch. In addition, there are two special types of sketches:

Planes Without Sketches

If you begin drawing on a plane that has no sketches, a new sketch will be automatically created for you. Once created, sketches can be used for feature creation, and they can be modified at any time using the various sketching tools.

Points are created automatically at the ends of 2D edges. The points can then be used for dimensions and constraints. Additionally, there are options in the Draw Toolbox to create a point at a screen location or at the intersection of 2D edges.

Deleting Sketches

Sketches may be deleted as long as they are not being used as input to subsequent features. Note that when you delete a sketch from its plane, the deletion operation is captured in the Undo/Redo records. Hence you may Undo the sketch deletion if desired. Also note that even though a sketch is deleted, its name is still checked when verifying the names of other items in the Tree Outline to ensure unique names. The sketch will stay in the Undo list until the modeled is saved, at which point the Undo/Redo records are cleared.