As far as the port goes, you need to know what port the server listens to.
You need to set a static IP for your computer (through your router), NOT ISP...although you do need a static IP if you want to "publish" your server, otherwise it will change and the old IP address will no longer work...I suspect (2 or 3 clients) means you only plan to use this with friends, in which case the non-static public IP isn't that big of a deal...it doesn't change often and when it does, just tell your friends.
But you DO need to have your router assign a static IP for your computer otherwise you will constantly be needing to reset the port forwarding on your router.
Basically, on your router find where it does port forwarding. Go to the routers setup page and you can probably figure where this is...if not check out this for help:
http://portforward.com/
What you want to do is to forward TCP port number (whatever the server listens to) to the IP your router assigns to the computer...that's why it should NOT be using DHCP. That website should also help you in setting up a static IP for your router.
Now I should say, that only ONE client can connect to the server at one time through a single port. There are two different ways to get around this:
1) connect to the server, get the information, then disconnect and then re-connect if you need more information.
2) have the server spawn a new thread that listens on some random port, send the port to the client, then re-connect through that port. I don't know how port-forwarding affects that, it might be that once the client connects to your computer it can use that IP to connect using the different port, or it might be the case that you need to have the server use a range of ports and make sure to forward all of that range (in the router) to your computer.