Customer registration
If your customers create an account with your store, then they can add their address information to their account so that it autofills during checkout. They can also view their order history with your store and see the current order status for any purchases they make.
From your Shopify admin, click Settings, then click Checkout.
Scroll down to the Customer accounts sections.
Check Accounts are optional and click Save.
Shopify provides a number of options for enabling customer accounts and you can find out more about this in their help article. See Shopify Customer Accounts guide here for more details about enabling this setting on your store.