Hi Marcelo,
You can process credit cards from the Receive Payment screen using a Payment Gateway, by checking the Process with payment gateway when saving? checkbox when creating the Payment.
If you don't have a Payment Gateway, you can set one up by navigating to Customize > My Account in Method, clicking (view / edit...) for "Payment Gateways", then clicking the Add New Payment Gateway button. Please note that you will need an account with one of the supported Payment Gateways. You can find out more about Payment Gateways, including which are supported by us, in this Help Center article.
- Justin