Shopify theme
A Shopify theme is the template system that controls how your storefront looks and behaves, built from sections and blocks you configure in the theme editor.
Themes are made of sections you can add, reorder and configure without code. Dawn and Horizon are Shopify's own free themes; the theme store and third-party developers offer paid options.
Most stores don't need a custom theme. A free theme with strong copy, good photography and clean information architecture outperforms an expensive theme with weak content.
Changing themes later means rebuilding your page layouts, so pick one with the section flexibility you'll want in a year.