The Scribble shape is one of the latest features added to the Tinkercad Basic Shapes menu. By dragging it on to your workplane, you’ll be given a new view that allows you draw shapes with your mouse pointer (or fingertip, if you’re using a touch screen). Be sure to check out some of drawing options across the bottom.
Once you’re finished, click Done, and your hand-drawn object will appear on the workplane. From here, you can further shape, extrude, reposition and resize your object until you’re happy with it. Or, switch your scribbled object’s mode from Solid to Hole and emboss your hand-drawn design onto another object.