The store tab under Settings displays the following fields:
Title: The name for the store to be displayed in the browser title toolbar.
Meta Tag Description: A tag providing a metadata description for the store. Meta tags are seen by search engines.
Template: Selects the template/theme of the store. OpenCart only has one, "default". Themeforest is a great resource for discovering 3rd party templates for OpenCart.
Default Layout: The default layout type for the store.
Video Tutorial
This is how the Store tab in the System Settings looks like.