Central to understanding merchandise configuration within MarketPowerPRO is the concept of products and SKUs (Stock Keeping Units). The software enables you to setup products (e.g. polo shirt), but the actual items that you sell and which are inventoried in the system are SKUs (e.g. XL green polo shirt, XL blue polo shirt, etc.).
Products themselves can be organized into categories for shopping display purposes while SKUs are organized according to the parent product that they belong to. For example, you could create a product category called "Clothing". Within the shopping cart, a user could view the clothing category. Inside that category, the user may then choose to look at the polo shirts. From there, the user could choose the specific shirt to buy - XL green polo. Pricing is controlled by SKU, allowing you to, for instance, charge more for the XL adult shirt then the children's M.
You can create as many categories, sub-categories, products and SKUs in the system as you like.