Heron's Formula provides a method to calculate the area of a triangle when the length of all three sides are known. It states that the area of a triangle can be calculated by taking the semi-perimeter (half the perimeter) and plugging it into the formula: square root of (semi-perimeter * (semi-perimeter - side 1) * (semi-perimeter - side 2) * (semi-perimeter - side 3)). This formula works for any triangle regardless of whether it is a right, acute, or obtuse triangle.