Listening To A Different Port?

So I have no idea how the whole router/port thing works. All I know is that the DSL is always fastest when it's simply stuck to just one computer and we get no wireless. But when I set up the wireless router and lock it, the overall speed drops to extremely slow. I have no idea what it means at all when it says I need to switch ports or something. What does it mean to check the listen port, firewall, or NAT router? I wish I have a computer guy on handy =_= *sigh* It makes me really mad to know that we're not getting the full amount of speed we should be getting because of the router. It's always like this after we put in a router. I wish I knew more about computers and all this online stuff =_=