There are two approaches to 3D sketching.
2D Sketching with 3D Sketch Planes. Activate a planar face by adding a 3D sketch plane, sketch in 2D along the plane, and add 3D sketch planes each time you need to move sketch entities to create a 3D sketch. This tutorial uses this approach.
3D Sketching. Open a 3D sketch, and press Tab each time you need to move sketch entities to a different axis. The sketch origin is placed wherever you first start the sketch.
2D sketches with 3D sketch planes allows you to:
Define planes
Add relations:
To planes
Between planes
Between sketch entities on different planes
Move and resize planes