Starting a Minecraft Server [duplicate]

Not sure what server launcher are you using (bukkit/spigot/original). But to do that, first you need to run the server.jar for 1 time.Then, everything will be set up(server.properties/plugins/world,etc.), then close the server.jar once everything is ready. You should see a folder called "world". Delete the world folder, copy and paste the world you created from .minecraft>saves to the server folder. Rename the world you pasted into the server folder to "world"(if the world name is not world, if it is, just leave it). Then run the server again you should have your world.