FASTER IN TURBOWARP: turbowarp.org/566813360?hqpen&fps=60 Click and drag to move the cloth. Use the mousewheel or up/down keys to change the mouse size.
Sometimes when you move the mouse too fast everything can go haywire. Just restart the project to fix it. If you're interested in how this works (and know a little bit of maths), look up "mass-spring cloth simulation".