1). Open a cmd prompt (Win+R, type cmd, press ok) and type IP config into the cmd prompt and press enter
2). Go to where you saved the server files, right click server.properties and open with notepad
3). Go back to the cmd prompt and copy your IPv4 address to where it says "server-ip=" in the properties list
*it should look something like this
{
…
force-gamemode=false
level-seed=
server-ip=192.168.1.141
max-build-height=256…
}
4).Forward port 25565 on your router and because I don't know the brand of router you are using I can't address this issue directly however I can send you in the right direction
http://portforward.com/english/routers/port_forwarding/
Hope this helps.
p.s. If you want to connect to your server you will need to
1). Go to google and type "what is my IP" into the search engine and copy the IP it gives you
2). Open Minecraft go to "Multiplayer" and press direct connect
3). Paste the IP you copied from Google into the box and connect