It’s very simple to make peanut brittle.
Place your corn syrup, water, and sugar in a 3-quart pot and bring to a boil. When the mixture starts to thicken, add the peanuts. Stir constantly while the syrup cooks to a golden brown and you can hear the peanuts pop or smell that they are cooked.
Take the mixture off the heat and stir in butter, salt, baking soda, and vanilla. The baking soda will cause it to foam but keep stirring until the foam goes down. Then pour onto a buttered cookie sheet and allow it to cook for several minutes.
The brittle is still very hot but pliable at this point and can be stretched by using either two buttered forks or pulled using cloth or leather gloves. Some people use bare hands that have been buttered, but the brittle is hot and I don’t recommend it.
Once the brittle has cooled, break it into smaller pieces.
Do you have to stretch the brittle? No, you could just pour the mixture onto the buttered pan and allow it to cool and then break it into smaller pieces. The benefit of stretching the brittle makes it stick to the teeth less.