There are two main possibilities to purchase a product. First one is Standard Checkout, and the second one is Guest Checkout.

Standard checkout: in the standard checkout you will need to create a new account or log in to an existing account, which offers additional benefits. Having an account connected to the email you have used for the order, you will gain access to your order history, payment details, and even more. 

Here you can check a tutorial how to purchase a product using Standard Checkout:

Guest checkout: this type of checkout allows you to make purchases without the need to create or log in to an account. By simply providing your email address, you will have a quick and easy way to complete your purchase without any registration hassle.