Sketches in 3D-CAD
3D-CAD supports two types of sketch—2D sketches that are created on a planar surface and 3D sketches that are built from points located anywhere in geometric space. You can use both types of sketch in 3D geometry operations such as extrude, revolve, or sweep.
Many of the operations for creating solid bodies take sketches as their inputs. For example, the extrude operation requires a sketch as an input, along with the direction vector in which to extrude the sketch.
Every 2D sketch is created on a sketch plane, which defines the position and orientation of the sketch in the 3D-CAD model.

Face Sketches
A Face Sketch is a 2D sketch that you create by extracting the edges of a face on a solid body. You cannot modify these converted entities. The link between these sketch entities and the face is retained so that changes you make to the body face are propagated to the Face Sketch. The sketch entities that are linked to the face cannot be edited through splitting or deleting operations, but you can convert them to construction entities.