Imagine carbs like a basket of apples. Some apples are sweet and juicy, giving you a quick burst of energy. Others are a bit tougher to chew, and your body doesn't absorb all their sugars. Net carbs are like counting only the apples your body actually uses for energy.
To figure out net carbs, you take the total carbs in a food and subtract the fiber and half of the sugar alcohols. Or you can use the below.
Fiber is like the apple core – you can't digest it, so it doesn't count. Sugar alcohols are kind of like those tougher apples – your body only absorbs some of their sugar. This is why net carbs are important on a keto diet, because they help you keep track of the carbs that really matter for staying in ketosis.