After you've created a free account, you have to log into your account, go to "Payments" section and select "Add funds". Choose one of the predefined option or click on "Other" and insert the desired amount. After choosing an amount, click on the payment method you desire, then click on "Next step" and "Confirm". After this, fill in your personal information into the credit card secured processing page.
You can add funds using the following methods:
VISA and Mastercard credit/debit card
PayPal crypto transfer (US only)
Crypto - BTC (Bitcoin), ETH (Ethereum)