Go to the category of the account you would like to purcahse , Add it to cart, and Checkout.
You will get all your account details on your email which you will provide during checkout.
You will get following details:
You can change steam password and email linked to the account. You can not change steam username.
You can pay via PayPal or Credit Card.
To pay using Credit Card, Checkout via paypal and you will find an option to pay using credit card. You do not need any paypal account to pay using Credit Card.