I understand that we break one of the multipliers down into smaller numbers. The number 12 is smaller than 452, and it can be broken down into 2×2×3.
So instead of multiplying by 12 we can progressively multiply by its factors to obtain partial products and finally end up with the full product.
Therefore, we start by multiplying 452 by 2=904 (first partial product)
Then multiply by 2 again: 1808 (second partial product)
And finally by 3: 5424 (final product).