Total Product is the summation of Marginal products at different input levels. When the Average Product is rising, the Marginal Product lies above the Average Product.
When the extra unit of output is cheaper than the average cost, then the Average Cost is pulled down. Similarly, when the Marginal Cost is greater than the Average Cost, the Average Cost is pulled up. The intersection between the Marginal Cost and Average Cost curves is also the minimum of the Average Cost curve. When the marginal output cost is equal to the average value of the output, then the Average Cost neither falls nor rises.