You know how when you go outside on a chilly day, your nose gets all snotty and your glasses start fogging up? That's because the cold air around you makes everything colder, and it can even make water in the air turn into little water droplets. Well, airplanes have the same problem - when they fly around in cold air, the air can make ice form on the engine, which can make the engine stop working.
To fix this problem, pilots turn on something called "carburetor heat." This is like a little heater that sits near the airplane engine and blows hot air onto a part called the "carburetor." The carburetor is like a little gas station for the engine - it gives the engine fuel so it can keep working. When hot air blows on the carburetor, it warms up the fuel and makes it easier for the engine to use. This helps the engine keep running even when there's cold air around it.
So, imagine you're eating a popsicle outside and your fingers are getting cold. You can blow on them to warm them up, right? Well, that's sort of like what the plane's carburetor heat does - it blows hot air onto something that's getting too cold to help it keep working like it's supposed to.