A credit slip is first and foremost a written proof that a product has been returned. Most of the time, the user can use it as a voucher.
A voucher is a discount code which does not have to be tied to a merchandise return or a refund, and which can take many more forms than a simple credit slip:
You can apply a voucher to all customers, or a group of customers, or a single customer; you can set its expiration date;
A cart rule is basically an advanced version of a voucher: in addition to what a voucher could do in PrestaShop 1.4, the cart rules system introduced in PrestaShop 1.5 enables you to:
- Carrier selection. You can make it so that the customer will have a discount if he or she chooses a specific carrier for the package delivery.
- Customer group selection. This is very useful. Thanks to PrestaShop's group creation tool, you can create discount that apply to a range of users, and build other conditions on top of that discount thanks to the cart rule creation tool.
You can go even further: with the help of modules such as the "Customer Segmentation" module, you have a set of very powerful tools to create cart rule, and make more clients happy. Download the "Customer Segmentation" module here: http://addons.prestashop.com/en/analytics-stats/2943-customer-segmentation.html
- Compatibility with other cart rules. Only appears if you have more than one cart rule.
- Product selection. Another very useful tool, which enables to create automatic vouchers for cart which contain specific products. The tool is explained in more detail below.
The "Product selection" option brings a whole new form, and enables you to create not only per-product vouchers, by also per-categories, per-manufacturers, per-suppliers and even per-attribute. As a bonus, you can combine all these in order to expand your customer target as much as possible.
The third and last tab, "Actions", is where you choose what the discount actually consists of.