First thing first when port forwarding is to know your internal ip address. You can do this by opening cmd (go to start menu and type cmd) and enter the word \"ipconfig\". A list of numbers and junk will come up, try to find the one that says defualt gateway. In front of it should be a number similiar to this: 192.168.x.x
(x\'s resemble any number).
Now that you have your internal ip, open up any browser and put those numbers into the address bar. This will bring you to your router settings. Next is to learn how to forward a port. Simply go to this link and find what type of router you have on the list. http://portforward.com/english/routers/port_forwarding/routerindex.htm
Now that you know how to port forward, forward the port 4242 in both UDP and TCP. (Sometimes theres an option for both or it does it automatically). You have now officially set up a server! Now to learn how to run it and let friends play on it.
This part is easy. First go to http://www.whatismyip.com/ and find out what your external ip is. Give this ip to your friends and make sure they put \" :4242\" at the end. Ex. 86.54.25.1:4242 (< not an actual ip). Then they will have to open up the launcher, press start game, and input this ip into the multiplayer tab. Before they do all this, make sure you, (or whoever the host is) opens up the starter.exe and clicks on the button that says \"start dedicated server\". This will launch the server. And lastly, to join the server yourself, (or whoever the host is), when you launch the startup and go to the multiplayer tab, instead of putting your ext ip in, click on the option that says \"local host:4242\".
~Best of luck!