If you just purchased a server you need to wait for it to be processed / delivered. This typically takes 30 mins - 3 hours. On your server dashboard you can view the status of your server. If it's pending the server has not been processed yet. Once the server show as Active the server is delivered and ready to go.
All server details are emailed to you automatically, if you did not receive the email for your server, you can pull up the details on the website by visiting here.
Your email will contain the server IP, the username and the password. This is all you need to connect to the server through any RDP client.