A theme is a template that determines the way that your online store looks and feels. Different themes have different styles and layouts, and offer a different experience for your customers. You can customize your theme settings from your Shopify admin by using the theme editor. If your theme doesn't have a setting for a change that you want to make, then you can edit your theme code.
What theme am I using?
A store theme's name can be found by going to Online Store > Themes from the Shopify admin. The active theme is shown in the Live theme section of this page.