First I do not recommend you to open a public server without the proper knowlege about the server software, configurating a webserver and so on. I would recommend you to create a local server on your system and then learn from it. If you just want to play with your friends use tunngle or hamachi it's saver and does not require a root server. In the rAthena Wiki you will find lots of guides on how to configure your server and many other things.
Here is a basic guide on how to setup a local server:
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Thanks for the reply nice