When you select a theme in ShopSite, the theme will have some default settings that it applies automatically. Each time you add a new page or a new product, that page or product is set up with those same default settings. Let's say you want to change some of those default settings such as the number of columns, or the product image alignment. After you make those changes, you want all new pages or new products to have those same default settings. In this case, you will want to go to Preferences > Page (or Product) Defaults, and change the settings to be what you want the default to be for every new page and new product that you add in your store from that point forward. These settings will not change existing pages or existing products. The video tutorial below shows how these settings work. You can also learn more specifics for the Page Default screen and the Product Default screen at the ShopSite Help links below.
ShopSite Help - Page Defaults
ShopSite Help - Product Defaults