A pot-holder is something you use to protect your hands when you are holding a hot pot or pan. Just like how you wear gloves when it's cold outside, a pot-holder protects your hands from getting burnt when you touch something hot.
Pot-holders are usually made from materials that can tolerate high temperatures and they come in different sizes and shapes. The most common pot-holder looks like a square pocket with a loop or a hanging hook. You put your hand inside the pocket and grip the hot pot with the material protecting your hand. Some pot-holders have a rubber or silicone surface to provide a better grip on the pot or pan.
It's important to use a pot-holder whenever you are handling something hot in the kitchen because you can seriously burn your hands if you touch a hot surface without protection. So, always remember to use a pot-holder when you're cooking!