Telnet is a user command and an underlying TCP/IP protocol for accessing remote computers. Through Telnet, an administrator or another user can access someone else's computer remotely.

Microsoft no longer includes the telnet command installed by default in Windows 7. It is still available but must be installed or enabled by the user. This can be done either using “Turn Windows features on or off” window found in Control Panel as shown below

Another way is through command prompt, below is the steps on how to do it.

Step I - Run "command prompt" as a administrator as shown below

Step II - Run following command as shown below

dism /online /Enable-Feature /FeatureName:TelnetClient

Step III - Make sure dism command complets successfully before you can use telnet