To wrench means to grab or pull something with a lot of physical force. See this teddy bear? If you want it, you’ll have to wrench it out of my hands, because I’m not willing to give it up.
Maybe you have a wrench at home, that is, a hand tool that is used to hold or twist a nut or a pipe joint. If so, you also have a great way to remember what wrench the verb means. Just imagine you're twisting with a wrench, except instead of using a tool, you’re using your hands. If something is heart wrenching, it makes you feel very sad. If you wrench a part of your body, you strain, pull or twist it, injuring yourself in some way.