Firstly you have to log on to your router setting thingee majiggee.
Well I don't know what type of router you have, but for me I log on to my router setting place and go to "Virtual Server"
Then there would be boxes where you can input stuff such as private port, public port blah blah blah

You'll need to enter ports 6881 to 6889, TCP and UDP server. then youll have to enter your computer IP, not ur internet ip, in the box where it says "HOST IP ADDRESS" e.g. 10.0.0.5 or 210.345.323 or something.

SAVE done.