I want to know how I can easily start a server that only me and my girlfriend who lives a few states away can play on.
Use a Virtual Private Network on both computers and have her connect directly to your IP if you turn your single player world into a server, or assign the server the IP address of your VPN client by modifying the config files and then both connect directly to it.
Hamachi is a good client to use, I've used it in the past with minimal problems.
This answer gives slightly more detail (also this is a duplicate of that question as someone else already pointed out): https://gaming.stackexchange.com/a/153532/103981
(This question is a duplicate, however, I will provide a detailed answer anyway)
There are multiple options you can choose to create a multi-player Minecraft server.
This information is from my personal experience, as I'm experienced with creating and hosting Minecraft servers from my own PC when I have wanted to play with friends.
The slightly harder option is to port-forward, however, you are looking for a way to easily create a server, so I will not go through that.
The easiest option out of the two I have pointed out (the option I would recommend you use) is to create a server over Hamachi -
- All players need to go to https://secure.logmein.com/products/hamachi/download.aspx and download the unmanaged version.
- Once it is installed, one of you will need to create a network with a login and the others can join the network using that login.
- The host of the server will need to copy the IPv4 address from their Hamachi by and share it with everyone else playing, or everyone else can right click the host in the network themselves.
- The host will need to download the latest version of the Minecraft server from https://minecraft.net/download under the heading 'Multiplayer Server' (the .exe is the easiest and most convenient so we'll use it in this case, but the .jar works for operating systems other than Windows, whereas the .exe does not). Note that if you are wanting to play on an earlier version of Minecraft, you will have to download the server corresponding to your version from http://www.minecraftforum.net/forums/minecraft-discussion/discussion/173960-minecraft-jars or you can look up "Minecraft old server version download" and you will find links to previous versions of the Minecraft multiplayer server available for download.
- Once downloaded, the host will place the file (.exe as we're not using the .jar in this case as it is more complicated and harder to setup) into a new, empty folder and launch the server.
- If you are using 1.8+, then once the server has been launched, a .txt file called 'eula' will be created. If this is not the case, then please skip to step 7. If this is the case, then close the server, edit eula.txt and change 'eula=FALSE' to 'eula=TRUE', and relaunch the server.
- Then the host will close/stop the server after it has performed a first time setup (creating the files needed, etc.)
- The host may now make changes to files such as 'server.properties' if they wish (this could be settings such as difficulty, enable command block, etc.) (these settings can be changed later, but the server will need to be restarted for the changes to take effect).
- Once people are happy with the settings, the host can launch the server and after it is launched, all players in the Hamachi network may join.