1)Download the Minecraft server software
2)Make a folder on your desktop
3)Place the server software in the New folder you made
4)Run the software (It'll give error messages, this is normal.)
5)Find the thing in the folder called server and open it
6)Go to http://www.whatsmyip.com
7)It'll give u a bunch of numbers with dots in between them.
8)Copy the numbers
9)Go back to the server folder and It will say Server Port:
10)The default server port is 25565, delete those numbers and paste the new ones.
11)Close the server software.
12)Open the software.
YOU HAVE A RUNNING SERVER!
Note:Your server IP will be those numbers you copied.