Here is an example below, 0.3 x 0.4= 0.12. All you have to do is fill in 3 rows vertically for 0.3, and 4 rows horizontally for 0.4. The part where the rows are stacked on top of each other is 12, then because you multiplied to decimals, move the decimals place for 12 to the left 2 times to get 0.12.