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