When making an order through Swapped, you're first asked to enter your email. You'll then receive a unique code to login titled 'Your Swapped code is XXXXXX'.
After you've entered this code, you'll be logged in to your account and you can make orders on Swapped.
You can also login without placing an order by clicking on the top-right and clicking 'Login'
If you've used a payment method, such as a credit card, previously on this account, this will be saved for future use to prevent you having to enter these details for every order.