Download the last multiplayer exe from Minecraft.net, for instance minecraft_server.1.8.1.exe. If you are running an older version of Minecraft (let say because you have installed an excellent shaders mod that’s still not updated to 1.8.1) don’t worry: it will work as well.
Move the minecraft_server.exe to a new folder that will be dedicated to the multiplayer. Or to the Minecraft installation folder if you want to keep it all together.
Execute the minecraft_server.exe. On my windows 8.1 laptop, the program launches but crashes immediately. This is because you must accept the EULA licence first.
In the same folder, open the EULA.txt and modify the last line with the ‘true‘ value:
#By changing the setting below to TRUE you are indicating your agreement to our EULA (https://account.mojang.com/documents/minecraft_eula). #Thu Feb 05 22:30:51 CET 2015 eula=true
Relaunch the minecraft_server.exe: that’s it, it stays open. Congratulation, you have a server running.
In your minecraft_server folder you will find a server.properties file: it contains all your server parameters, for the game (number of players, gamemods, difficulty etc.) as for the server (welcome message, server port etc.) Modify at will, if you find it necessary.
You may want to load your solo map as your multiplayer playground. To do so copy your save (C:\Users\User\AppData\Roaming.minecraft\saves\xxx) to your multi folder, at its root. Delete the /world folder. Edit the level-name=world line of the server.properties file.
Launch minecraft_server.exe, then launch the game and go to the “Multiplayer” section. Your server name and welcome message will appear on top.
You are now ready! Send your server name and public IP address to your friends, they will have to enter it in the “Direct connect” section of their multiplayer screen.
Have fun, and try not to trap your friends houses with dynamite.