What is telnet?
Telnet stands for 'Teletype Network' and is a network protocol. With the help of this protocol you can get access to another computer or network component. This is done through the Telnet client, which establishes a connection to the Telnet server.
How do I use Telnet?
The Telnet session is established by entering the computer name or IP address. These are transmitted via a TCP port 23, followed usually by a password request. With the terminal protocols can be addressed directly. Thus, connections to remote servers are established with the commands and various data or even databases can be accessed.
An example for a Telnet client is Putty. You can download it here here. After downloading it, you can specify your domain and 'SSH' or 'Telnet' as protocol. With Putty you can now establish text-based remote connections via the terminal and issue commands.