Advantame is a type of sweetener, kind of like sugar. But instead of being made from sugar, it's made from chemicals.
When you eat things that are sweetened with advantame, your taste buds think you're eating something sweet like sugar, but your body doesn't get any calories from it. This means that it won't make you gain weight like regular sugar does.
However, just like anything else you eat, it's important to not have too much of it. So make sure you only eat things with advantame in moderation, okay?