Customer Registration

Customer accounts let your customers log in to view their orders, profile information, and saved addresses. When a customer logs in, the details stored in their account are auto-filled during checkout for a faster checkout experience. Please read more in shopify well written detailed article

Steps:

1. From your shopify store Admin -> Click Settings -> Locate Customer accounts

2. at Accounts in online store and checkout, click edit

3. choose "Show login link in the header of online store and at checkout"

4. 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.