Starting a 3D sketch is easy. Use the Insert pull down menu and select 3D Sketch.
Once a 3D sketch is started, the Tab key can be used to flip between the available directions in which we can sketch. Notice in the image below the cursor does not list Z as an available direction for sketching.
Hitting the tab key, switches the available directions. You can see based upon your cursor feedback that the Z direction is now available.
3D sketching using this method requires you to be aware of your available directions and orientation in order to get the desired outcome. Now let’s use viewports to make specifying directions and viewing the overall orientation easier.
Using a Four View Viewport eliminates the need to use the tab key to switch sketch directions. Simply go to the viewport that has the associated direction and sketch. A bonus feature is the trimetric view of your 3D sketch for easy orientation visualization. As you are sketching in one viewport you will see the other three update simultaneously.