The valve module is how you get your section control. You can bank as many clutches onto one valve as you want so that you have total control over your sections.

Valve module boxes each contain 4 valves. One module box will give you 4 sections.
As an example, if you have a 16 row planter and wish to split it into 2 row sections, you will need to purchase 2 valve module boxes. This will give you (8) 2-row sections.