Well depends on where you want to host your server. At home or on a real server. I mean it is not that usefull to host a server at home since your internet connection will not be good enough to provide a lagfree environment.
If you want to host it at home you will need to forward ports in your router to the computer that runs the server.
https://en.wikipedia.org/wiki/Port_forwarding
Also you will need a way to update route a static hostname to your dynamic ip so your client can does a constant he can use to find your server. There are many solutions this for example:
http://www.noip.com/
Otherwise you could rent a Virtual Private Server or a Root Server. Those are servers that run 24/7 and are connected to the internet by default with a static ip and also have the hardware and connectionspeed to provide a good server expierience. But i guess Root Servers are a bit pricey and VPS often lack the power to run a big server.
If you want something like the above but with less work and maybe a bit cheaper you could look for the hosting services here that specialized in hosting ragnarok servers.
Also if you host at home, a root server or vps you have to do everything alone, especially the security and stuff. You could go for a managed server too, where they take care for that, but that is quiet very expensive. You shouldn't take that lightly since it is your responsability what happens on your server and the things that can happen when they are compromised and missused.
I gues thats another point where you are better of with a ragnarok hoster since they provide play ready servers where you just have to take care of what you want to achieve.
