Remember that a catalog price rule will apply to all the products that meet its criteria. After you create and apply this rule, it will affect your entire catalog (at least, the parts of your catalog that meet its criteria).
You probably want your catalog price rule to apply to only specific products. In our example, we want the rule to apply to only coffee products. All of our coffee products use the attribute set coffee-by-pound. We will filter our products by that attribute set, so that the catalog price rule affects only coffee products.
Before you create a catalog price rule, you must decide which products you want the rule to affect. Then, you must determine what those products have in common. Do they all have the same attribute set? Do their SKUs begin with the same characters? Are they all in the same category or categories? Investigate and write down the criteria that you will use to filter the products for your catalog price rule.