Numbers contained in the rows of the A matrix are multiplied by matching columns of the B matrix.
For full definition, see Wikipedia.
Enter numbers in the blank fields of matrices A and B. If inputted matrix has less than 3 rows and columns, leave the unneeded row/column blank. If a matrix has more than 3 rows or columns, click the "+column" or "+row" text to add new fields which you can fill with numbers. Maximal number of columns is ten.