It's a visual aid for multiplication.

You make a line group for each digit in each number. In your case, the first number's lines are going right and up and the second number's are going right and down. Highest digits start on the left. If you make the diamond shape, evenly, vertical slices of the intersection groups correspond with the 'no-carries' multiplication that goes into the corresponding output digit. First you sum these, then you pull off the lowest digit for each output group starting rightmost, and add any additional numbers to the next group to the left.

Is that enough to get the bounty?

e.g. 12 * 34

2*3

1*3 2*4

1*4

=

6

3 8

4

= 3, 10, 8

= (3+1)(0)(8)

= 408

If this is good enough, coins go to: 1bgc1FDPgANFsGcNcnmzpYKHrp7SWMgaZ