1: The easiest way to create a new customer account is simply going to your registration page and filling in the account creation form and hitting the create button:

 

2: Once the customer has been created in your account, simply click on Order > Create Order inside of the Shopify admin panel as shown below:

 

3. Select any product by clicking the browse button (or if have no test products, select "Add custom item" and just make a test product that way) and add it to the order. Next search for your email in the Customer section, and choose the email for the customer account you just created. Then mark the order as paid.

 

4. You should then see the Create Order, press that (as shown below) and the order will be added to your account to view in the customer accounts.

 

5. You now should see something very similar to the screenshot below showing you Customer Accounts Hub.