The first pen tool, the upper left corner of the mode jump to the "path" (the default is the shape layer), with ctrl, shift, alt shortcut to outline the lines, note that the foreground color is black, brush transparency 100, flow 100, brush diameter 2 or 3 elephant rope. Right-click to select the stroke path, tool selection brush. Or click the brush tool, directly back to the car. You can check Analog Pressure in the Stroke option, which will appear as lines of different depths and thicknesses.