Often on your eCommerce website,you might want to allow users to anonymously checkout that is allowing them to place an order even though they are not a customer of your website. There are number of reasons on why you allow anonymous checkout which you can read more about here.
This post will show you how you would enable anonymous checkout of Sitefinity eCommerce 4.2.
The Checkout widget controls the checkout process in Sitefinity eCommerce, so when you drag and drop Checkout widget on to your page, hit edit for bringing up the control designer property screen
Hit advanced button on the control designer to bring up advanced properties. In the list of properties of checkout widget there is a property called CheckoutRequiresLogin, by default this value is set to true which means, every user that will checkout using your website will need to register with your website. But if you change the setting to false, the eCommerce system will allow users to checkout even though they are not a registered user of the system.
Below is a screenshot of where the property is on Checkout Designer properties.

Hope this helps
Cheers
Venkata