If you don't have a Digital Ocean account, you can sign up at https://cloud.digitalocean.com/registrations/new.

You can sign up with your Google account, or by registering manually. Once you register with Google, you will see the billing info view, as follows:

You can pay with your credit card or by using PayPal. Once you configured your payment information, Digital Ocean will ask you for some information about your project so that it can configure your Droplet faster: