If you are stung by a jellyfish, it is important to remove any tentacles that are still attached to your skin. You can do this by gently scraping them off with a credit card or other flat object. Next, rinse the affected area with salt water (not fresh water, as this can make the sting worse) and soak it in hot water for 20-45 minutes. If you are experiencing severe pain or other symptoms, seek medical attention.