index.liquid template renders the home page of the store. The template is loaded when you go to the root ("/") of the store.
Accessing the attributes of a specific object
index.liquid template, you might want to show the contents of a specific object. For example, you might want to showcase the Frontpage collection on the home page. This is done by passing the handle of a specific object or through a theme setting variable. See Accessing attributes with the handle for more details.