if you have CSS Form Builder 2 installed, that contains all of the functionality of Universal Email 4. you should not install Universal Email and CSS Form builder 2.
you will need to uninstall them both, then reinstall CSS Form Builder 2.
When you run the checkout wizard, if you select one of the Local checkout methods (Like PayPal Pro) It will automatically configure the checkout to send an email using Universal Email.
if you select a remote payment method, the Gateway will handle sending the order receipt instead of Universal Email, this is because the Remote checkout methods do not process transactions in real time.