(Windows 7 Users)
**Note that this is a guide for Windows 7 only if you need to know how to do it through Mac or another type of computer just let me know and I will write that up for you. :) **
1. Login into your router here. If you wanted to write it down it is http://www.routerlogin.net or it can be .com on the end of the url address but it really doesn't matter. The username should be admin and your password is password. Too easy right?
2. Go into the advanced settings tab. Then all the way at the bottom click advanced setup.
3. Click Port Forwarding/Port Triggering. Where it says Server IP Address you want to type your computer's IP. In order to find that click the start button and where it says search programs and files type in cmd.
4. A black window should come up. Type in ipconfig/all and press enter. Scroll down and look for IPv4 Address. That is the IP address you will need. Type in those numbers where it says Server IP Address on your router settings and click add.
5. Click on the service and click edit service.
6. Type in 25565 in the external starting and ending ports. Then click apply and thats it you're done with the hard part.
7. Next open your minecraft server and you can test it out by logging into the game and going into multiplayer and adding localhost and it should work. In order for your friends to login into it all they will need is the IP address you used to port forward it with.