Modern Store is absolutely a template for an E-commerce site. It's a free WordPress theme from CompeteThemes that helps you build an online store in a minute.
The simple, minimal and clean design makes Modern Store a safe choice for any site. If you are a beginner and don't know how to use and set up a store with WooCommerce, don't worry as it's well-documented and has dedicated support from the author.
If you are looking for a basic and simple E-Commerce site, don't need to look further, Modern Store is a good move. Thanks to the simple and airy design, you can sell anything without any fear at all. The speed is quite okay that you don't need to think so much about loading time.
However, it's not a feature-rich theme so you shouldn't expect too many things from it.