I'm quite unsure if it is a good idea to help you?!
But I will help. I'll show you how to set it up both ways.
A small notice up front. Telnet is quite old, has no encryption and is a guaranteed invite for a hacker. So if you can avoid using telnet, please do so!
1. Connect from Windows to Ubuntu with telnet
Telnet server won't work by default because it is insecure and therefore not installed by default. To do so, do the following:
sudo apt-get install xinetd telnetd
This will install the telnet server. After the install you should be able to connect to your ubuntu server from windows.
2. Connect from Ubuntu to Windows
To connect the other way, you need to have the telnet client installed on Ubuntu. As telnet is considered insecure, the telnet client also is not installed by default.
apt-get install telnet
After that you should be able to connect with the telnet command from the console.
3. Troubleshoot connection
If this doesn't work you will have to troubleshoot your connection.
Make sure Ubuntu isn't stopped by a firewall
Just check if the Ubuntu firewall is enabled
sudo ufw status
and disable it for the time being, if it is on
sudo ufw stop
and you should probably allow the tcp port
sudo ufw allow 23/tcp
Use nmap to test if the windows telnet service is available
sudo nmap -sS your-server.here
If you can't see the port listed after the scan, the problem is with your windows machine.