Set up commission matrix formulas, load percents, deductions, effective dates and splits on the Matrix page of the Salesman Master. You can also configure it from Sales>Salesman Commissions>Salesman Commission Matrix.
Before setting up your commission matrix, there are some underlying concepts and settings you should understand:

DDI System configures a number of sales commission default settings during implementation. You shouldn't change these without consulting DDI Customer Care, but see Default sales commission settings to understand how the default settings will impact your commission calculations.

Commission Structure Groups allow easy set up of salesman commission matrices by letting you set them for groups instead of having to set each commission matrix for each product individually. While you can set individual commission matrices on the salesman/product level, you can also set the commission matrices on a much broader level saving time and effort. Commission matrices can be set for each salesman and and combination of product lines, price groups, buy lines, major groups and vendors.
For example, if you want a specific salesman to receive a 25% commission on each product he sells from the Clearance price group, you can set the formula so that the commission will be automatically calculated when the payment is received. Groups help you organize your commission structure, which you should consider before setting up the commission matrix. See Organize your detailed commission structure.

As Salesman Commissions are set up, they may be calculated based on a number of combinations and relationships between the salesman, the customer, product, and commission groups. Each of these combinations are associated with a salesman matrix level, ranging from level 1 that is very specific (salesman/Customer/Product/Branch) to level 26 that is very broad (Salesman). These factors work in combination to determine the final commission. Levels define which commission formula is used based on the priority. See Sales commission levels.
You can then