It is pretty simple really.
First, go to your router, type in 192.168.0.1 into your url bar either in IE or firefox or whatever browser you use. It will be this or 192.168.1.1, 192.168.2.1 etc, just change that number up each time until you get prompted for a user+password. You should have this with information with your router, on the base of your router or with the broadband package info your isp should have provided.
If it hasn't i am guessing it is the Verizon FiOS ActionTec MI424WR router that you have, if so, the default username and password is:
user:admin
password

assword
If this doesn't work try same username but
password

assword1
If this still doesn't work and you don't know the pass then on the back of your router press the reset button. If you have mac adresses in your router you will need to put them in again, but unless you know the pass, this is the only way.
then the username will be:admin
password

assword
Ok then, once you are in, find the port forwarding area of the router and put in the port that warcraft uses, i think default is 6114, but to be sure (it is important that you get the right one) go into WC3 and at the start up menu go to options and i think it is gameplay, it should have port number there, that is the port you need to put forward.
http://portforward.com/
Go here to check how to get to port forwarding on your specific router.
Once you have done that, you should be set and ready to start hosting