In order to run an online store, you first need a domain name and web hosting. If you don’t want to build the website yourself, you will need a content management system or eCommerce platform on which to build it. Some eCommerce platforms will provide hosting as part of the package. Additionally, you will need payment gateways to collect payment for products and some type of shipping and fulfillment plan for delivering items to customers.
That’s the bare minimum though. For customers to feel secure on your site, you will also need an SSL certificate. To facilitate organization between your offline and online inventory, you may also want to integrate to your POS system and have an inventory management system or warehouse management system. You may also want to include marketing tools and SEO to help potential customers better find your site.