Creating a Minecraft server using an already existing world

First time user of the AMP panel, I am able to creat and start Minecraft servers, but I have a single player world that I have been playing on for a while and I would like to create a server using that world so that other people can join the server. So how can I create a server with the world folder of my single player world

See the cross post: Customization with Minecraft - Creating a Minecraft server using an already existing world