when using a router to connect to slsk, it is preferable for port 2234 to be open, usually 2 users connecting via router should be able to connect to each other if only one has 2234 open, but not always. thankfully someone on the slsk forum created a page which lets you know your ip, if your port is open and if the server is up. it can be found here
if your port is closed and it is preferable to be open, there are a few things you need before attempting it. your ip, the address of your router (the internal ip) usually 192.168.1.1
and also your router login details, including the username and pass. which will be default if the person who set it up for you hasn't changed them.
end of part one... more to follow