unmodded) server that will do weird shit. If you do, you will start a vanilla (i.e. ALWAYS use the script, never manually start the server.jar. If you were wondering, launch.bat is your launch script on Windows, while launch.sh is the one for Linux/Unix/MacOS.Edit the launch script and change the -Xms (minimum) and -Xmx (maximum) allocation values as needed. If you need it to work for more than just a couple of friends, give it more RAM.Even if you let it generate a world, the name that you set here will be used, default is just "world". You need to set the world name in server.properties to the exact directory name of the worldsave for it to use the existing one.
If you want to import a singleplayer world, locate the worldsave and copy it over to the server directory.Edit your server.properties file with all the settings you need.This will not (ever) work if your ISP puts you in the baby cage that is carrier-grade NAT, so let's hope yours doesn't. To have it work across the Internet, the server needs to have the port it will listen to (default: 25565) forwarded from the router. If you are all on the same home network (LAN), this should just work. Make sure your clients can see the server.
This will work side-by-side with a client installation, but unless your PC is a high-end monster, it is much recommended to use another PC for the server, if any is available.