Where is the Server Directory?

Solution 1:

You'll need a server to do this (unless they're on your LAN, in which case loading the world and opening it to LAN should work). You can get one from the Minecraft website for a basic server, or get a Spigot server for something a lot more advanced.

Assuming you just want a base server, you can set one up fairly easily, and this guide explains it better than I could http://minecraft.gamepedia.com/Tutorials/Setting_up_a_server

As for adding the world to that, you can just put it in the same directory as the server JAR itself, and configure the server.properties to reflect this.

The server directory is wherever the server JAR is executed from. Everything from here will be relative, so within this folder is the configuration file server.properties, the world save folders, and the where the logs are saved.