Tutorial: how to use freeform command
Click on freeform command. Then select the surface that you want to shape. then click on add curve button and add curves. They don't have to be equally spaced. If you want to add horizontal curves, click on flip directions button. if you make cordinate system user defined, you can add cross curves. completely up to you
Then click on add points button. add points on curves that you created before
if you want to make large wrinkles, make closed the points each other
Now we are at most important section. You have to hold and drag the points. it needs a bit skill. You must follow wave of wrinkles.
Use same command on other surfaces. This command is more difficult than make a engine for me. it is completely freeform:))