right heres a few simple steps:

First open you bit torrent client and go to options and look to see what port it is listening on it will be a random port. Make a note of this for later.
Then go to start and in the search at the bottom type cmd and press enter.
This will bring up a command prompt and type ipconfig.
You want to look at the top of this commands output and you want your default gateway. This will be an ip address like 192.168. * . *. Type this into your internet explorer this will take you to your routers home page.
Login if necessary and go to advanced and then admin or firewall or application are the most common one.
You will then be able to add the bit lord client and set the port.

If that dont work pm me and tell me what router you have and your bit torrent client and i will help you further.