If your server runs Linux as its operating system, you must use a terminal program, such as PuTTY, to access it. If you want to access your server from a Windows machine, go here and download putty.exe (the first file available for download).
http://www.chiark.greenend.org.uk/~sgtatham/putty/download.html
Then, enter your IP address in the Host Name (or IP address) field and click Open.
You will receive a PuTTY security alert. Click Yes. This will connect you to the terminal screen for login.
Now type: root
as the username, press Enter, then enter the provided password. You are now logged into your server.