Sadly, at the moment Semplice does not currently offer ecommerce integration with Semplice since we're focused mostly on design portfolios. Third-party plugins such as WooCommerce are not compatible either.
That said, you can still link out to third-party ecommerce platforms such as Shopify or BigCartel, for example, from Semplice.
Creating an e-commerce link from the menu
You can add a button in your main navigation that can link to your e-commerce site or store as a custom link. To add a custom link, go to Customize > Navigations and select your navigation bar.
In the navigation options, under the Menu tab, select "Edit Menu Items". Then click "Add Menu Item" and set the Link Type as "custom". Add the custom link to your e-commerce site homepage and add it to your menu item.
You may now wish to custom style this particular menu item different than your other menu items, since it is a call-to-action button. You can follow this guide to learn how to custom style a particular menu button with a little CSS.
Creating an e-commerce link button on your page
You can add a button to link to your third-party e-commerce site anywhere on any of your pages via the button module. You can learn how to do this here.