like here, http://simutrans.fr/doku.php?id=en:tuto:reseau:mini_reseau

tested and working :)

This is only true, if you are in the same network or on a computer with a permanent internet connection (like in a university). If you have to traverse a router your need to make sure simutrans packets reach simutrans (default port is 13353, which meed to be forwarded to your computer). Additionally, you need now your external IP. Or try hamachi for networking.
If you have a working IPv6 connection you can use the IPv6 address with the method given in the link, but this is seldomly the case.

and theres nothing about the firewall? beucase all the games i want to start a server just nobody can enter and peple tell me about firewall

The linked tutorial is just for a server in a local net. If you are behind a router, then you need to log on the router an set up a port forwarding for IP port 13353 to your computer.
The firewall will ask automatically, if you want to allow Simutrans internet access. However, in order to start a server, you have to do it with a shortcout where you add "-server" to the commandline arguments, not via steam.