Adding a domain to your Shopify account
In your Shopify admin, domains have been moved from the Online Store page to the Settings page. Go to Settings > Domains to manage your online store's domain settings. When you join up for Shopify, your online store is given a myshopify.com URL by default. You can customize the web address that clients see when browsing your store.
A subdomain is a subset of your main domain that you add as a prefix to your domain. If you have a Shopify Plus account, you can add up to 1,000 subdomains to your store. A new SSL certificate is immediately created for free when you add a domain to Shopify.