The default order method for product lists allows you set the order in either ascending or descending order.  The following tutorial will guide you in setting the default order method in the Prestashop 1.5 Administration Panel.

Set the default order method for product lists in Prestashop 1.5

1. Login to the Administration Panel as an Administrator
2. Hover over the menu bar where it says PREFERENCES, and then click on PRODUCTS in the drop down menu. Scroll down the list of options and look for Preferences: Products.  Select DEFAULT ORDER METHOD in the menu as shown below:
   
   
   
   
3. Click on the drop-down menu and select the default order method - ASCENDING or DESCENDING - that you wish to use
4. Select the green SAVE button in the top right hand corner

The default order method allows you to determine the order that will first appear when the product list is displayed.