[HELP] With my Windows-Router.

that means portforward
Read this: http://portforward.com/english/routers/ … /eMule.htm
It uses emule, but it's the same as teeworlds server.

Open a web browser like internet explorer or Netscape. Enter the ip address of your router in the address bar of your browser.

In the picture above the address bar has http://www.google.com in it. Just replace all of that with the ip address of your router. By default the ip address should be set to 192.168.1.1.

You should see a box prompting you for your password. Enter your password now. By default your password is 1234. Click the Login button to log in to your router.

Click the Network link near the left of the page.
You should now see a new menu. In this new menu, click NAT.
Click the Port Forwarding button near the top of the page.

Select User define from the Service Name drop down box.
Fill the form:

Ports used by Teeworlds are from 8300 to 8310.
The server ip address is the internal IP of the computer running the server. If you use windows, type ipconfig, under linux, ifconfig, in the command line or terminal.
Click the Security link near the left of the page.
You should now see a new menu. In this new menu, click Firewall.

Remove the checkmark from the Active Firewall checkbox.
When you're finished, click Apply near the bottom of the screen to save your changes.
And that's it! You're done!