Can someone teach me How to open server? I really want to play with my friend via internet :(

[HuGoGGB]

I've been tried -D to create dedicated server but my friend cannot see it online. My ip address in game've showed 192.168. So I think that would be LAN in my computer only.
Hope someone helping me I want to play with my friend so bad.

[odisseus]

Why don't you just use one of the public servers? Most of them are empty most of the time.

[Brumi]

You need some port forwarding to do that. Forward your port 3979 (both TCP and UDP) to your computer, then tell your friend your router's external IP. Or, if you forward the port 3978 UDP as well in addition to 3979, you can set the server to appear in the list of Internet servers. Additionally, if your antivirus software has a firewall, you may have to set OpenTTD as an exception to allow it to accept connections.

If you don't know what all this means, then you should read this first: https://en.wikipedia.org/wiki/Port_forwarding Also, the way you do it depends on the manufacturer of your router. You should search the Internet how to do port forwarding with your specific router.

[mauried]

If you type whatsmyip into most web browsers, it will tell you what your public IP address is , which is the address that your friends will have to connect too.
You will also have to port forward your router as Brumi has suggested.
There are some circumstances where this method wont work and its usually if you are connected to the Internet via a wireless connection where you arnt given a public address at all, are are given whats called a CGNAT IP address.
In these circumstances you can still play OPENTTD in multiplayer mode, but you cant host the game.