The payment details page shows your billing address, and your VAT number. If you are outside of the UK, but within the European Community and have a VAT number, you can enter it here for non-VAT payments.
You can update the billing contact here to another user if you wish. The user will need to be an administrator with an activated DeployHQ account.
You'll also be able to enter your card details to be used for ongoing subscription payments, as well as any discount code that you may have been provided.
Additionally, if you wish to make ongoing payments less regularly, you can update your Billing Frequency. You can choose any number of months up to and including annual payments.