All depends the make and model of your router as well as what type of firewall that you are using.
If it is a linksys router you will go to your routers ip address 192.168.1.1 and enter in the password (username is blank) which is by default admin if you never changed it. You will go onto a tab called applications&gaming. Here you will put the mentioned ports in and the local address of you computer. (to get this open up a command prompt window by clicking on the start button and clicking run, then type cmd then click ok. You will then type in ipconfig, your ip address will be a 192.168.1.* number)
This will forward the ports on your router.
If you have a firewall you will again have to open up the ports to allow the traffic through. Not knowing what type of firewall you have i couldn't even begin ot put up on how to do this. You could try turning if off and seeing if your friends can connect.
P.S. Sorry if this does not make sense possibly wrote this very quickly before I went to bed.